Defending caches against metal detectors

Discussion in 'General Survival and Preparedness' started by Oltymer, Jul 1, 2016.

  1. Oltymer

    Oltymer Monkey++

    I have been actively using metal detectors since 1964 when I first acquired a Fisher BFO unit. Over 40 years of detecting experience and I never found anything but rusty nails ( I'm sure there are IRS agents here besides all the other feds). So, I am going to share some insight on defending your cache against metal detectors, and that should be multiple caches, always bury in 3's.

    I only met 1 LEO who was actually good with a detector, it takes experience and skill to operate one with any degree of success. It also takes a lot of energy swinging that coil and concentrating on what the machine is trying to tell you. So, a new guy with an out of the box detector is practically no threat against finding your hoard, even someone with a few years of experience can be easily defeated.

    Detectors went through an evolution over the years, starting with BFO (beat frequency oscillation) from the WWII era through about 1974,, then TR (transmit receive) from the early 70's through mid 80's, then VLF (very low frequency) , with the newest units being digital VLF, also development of PI (pulse inductance) units, which are only really useful in salt water or on salt water beaches, amongst a host of late comer designs. I have used them all to find nails, and they all have their strong and weak points which I won't go into here.

    First is depth, VLF's have great depth reading capabilities, but it is all dependent on the diameter of the coil they are using. Standard coil sizes run at about 10", but 20" coils are available. The larger the diameter the coil, the greater the depth. The drawback is that the larger diameter coils are also high energy, and will soon wear a guy out swinging them with all that weight out on the end of a rod, it multiplies the amount of energy used in operation. a 30 cal. ammo can be detected with a 10' coil at about 18", with a 20" coil, that can be as deep as 3'. Detection is deeper in wet soil than dry soil.

    #1 tip is masking, for instance if you have 100 oz. of silver, buried in a glass jar, or leather sack, or PVC pipe, the detector will easily read the silver, and you lose your stash, but if you put the silver into a steel container such as a ammo can, the detector will tell the operator that there's a steel object below the coil, not silver, as the electromagnetic eddy waves coming from the coil can only read the outside surface of the buried object. Of course he has the option to dig and explore the signal which leads us to - tip #2, which is to bury many objects of steel that will wear the detectorist out from all the fruitless digging. Lots of tin cans, railroad spikes, horseshoes, rebar, etc. Aluminum is easily differentiated from steel, so aluminum will not work, unless your cache is also inside an aluminum container, then all those empty beer cans can serve sentry duty for your stash.

    Detector coils read down into the ground but also have an equal effect above the coil, so for instance you decide to bury your stash below a metal gutter downspout the guy detecting will have to rip the downspout off to see what is below it, same goes for all those aluminum air ducts below your home, if you have central air.

    Assuming that threat forces will be using the most up to date and expensive units, which will be digital VLF. These are great machines, and are capable of telling the operator what kind of metal is beneath their coil, but are lacking in telling the operator the size of the object being detected. A nail sounds just like a 5 gal steel can as they have difficulty reading how big the object is with a digital unit, but they can tell how long it is, so a rifle would read as a long steel object. So try and eliminate the long target signal by burying it on end, which reduces its target area and profile, also bury some rebar and iron pipe just for giggles.

    There is more, but it's the Fourth, and I'm deep into a 5th, so ask any questions and I will be happy to try and answer them. Cheers, and have a safe and happy 4th!!

    Last edited: Jul 1, 2016
    BenP, Gafarmboy, Sgt Nambu and 17 others like this.
  2. 3M-TA3

    3M-TA3 Cold Wet Monkey

    Excellent information. I've been wondering about this subject for a while.
    Altoidfishfins likes this.
  3. Capt. Tyree

    Capt. Tyree Hawkeye

    Useful information for both the cache buriers and the rusty nail hunters.:) Thank you for the benefit of your experience.
    Ganado likes this.
  4. MountainMariner

    MountainMariner Clearly Ambiguous

    Leave a very long trail of pennies leading away from your cache...

    A penny every five feet for a mile should keep them busy.
    chelloveck, GOG, Ganado and 2 others like this.
  5. Salted Weapon

    Salted Weapon Monkey+++

    Awesome post and great information.
    When I drink on the 4th I tend to plead the 5th. ;)
    GOG, Ganado, AD1 and 2 others like this.
  6. Bandit99

    Bandit99 Monkey+++ Site Supporter+

    Priceless information. We owe you!
    GOG likes this.
  7. oil pan 4

    oil pan 4 Monkey+++

    There are pieces of metal from steel fabrication work, copper pipe pieces, brass bits, lead, stainless steel cuttings, a ring of roofing nails encircles the house the rest are all over my yard they would have to dig up the whole thing.
    GOG, AD1 and Oltymer like this.
  8. Oltymer

    Oltymer Monkey++

    Yeah, anything built in the past 100 years has a ton of construction junk all around it already, believe me I know from digging all those rusty nails! I'm always shocked at what the plumbers and electricians have left laying around in the form of copper, not that I've ever found anything of value, but what others have found. hahaha!
    chelloveck likes this.
  9. oldawg

    oldawg Monkey+++

    Thanks Oltymer, I've been wondering if my rusty nails are safe and it seems I have some more work to do.
    Yard Dart likes this.
  10. chimo

    chimo the few, the proud, the jarhead monkey crowd

    Good info...though I think you are farther into that fifth than you think, since it's the only the second, maybe the third in some locales, but not yet the fourth. ;)

    One great way to protect your caches from metal detectors is to not have your caches where they are expecting to find a cache or where they have a warrant to look for them. That's all I got to say about that.
    Bandit99 and GOG like this.
  11. arleigh

    arleigh Goophy monkey

    I have trouble enough tryin to remember where I put regular things much less what might be hidden under ground some where. I'd need a treasure map to find it all again .
    Thanks for the insight on metal detectors though .
    I have an old radio shack unit I haven't used in years ,it takes a fist full of 9 volt batteries, probably why I didn't use it much.
    I often thought that having a bunch of decoys might be useful burying things on end is a great idea, thanks.
  12. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Even my water district has a Ground Penetrating Radar rig for finding water lines buried over two feet underground. Don't doubt that when they come to confiscate that they will utilize that technology over a metal detector.

    GPS Cache your goodies in the National Forest... Nobody is going to look there.
    Bandit99, GOG and Ganado like this.
  13. Oltymer

    Oltymer Monkey++

    002. 002. 1 picture is worth 1000 words, so here's 2 pics. 001.
    Last edited: Jul 2, 2016
  14. Altoidfishfins

    Altoidfishfins Monkey+++ Site Supporter+

    Interesting...the soil at my BOL is loaded, just loaded with magnetite. Don't drop a magnetic screwdriver if you don want to clean up the mess.

    I tried detecting there, and the detector just goes of everywhere. It's not a cheap one either.
    Oltymer, Dunerunner and Ganado like this.
  15. Dunerunner

    Dunerunner Brewery Monkey Moderator

    Sounds like a perfect location!! [winkthumb]
  16. GOG

    GOG Free American Monkey

    Thank Oltymer, that's good info.
    Dunerunner likes this.
  17. Gator 45/70

    Gator 45/70 Monkey+++

    I'm burying mine in an old WW 2 practice bombing range.
    Lets see just how big a set those boys have finding mine!

  18. natshare

    natshare Monkey+++

    Great info, @Oltymer ! One thing I've thought about (but have no idea whether it would work) would be stashing something in line with old galvanized steel buried water lines, or cast iron/steel drain lines. If your cache (say, a rifle, wrapped and stashed in a PVC pipe capped on both ends) were laid right on top of that steel line, would the metal detector see the difference? Or, conversely, if it were stashed underneath the metal pipe?

    Seems if they were following a line for more than a few feet, the operator would deduce that it's a buried water or waste pipe, and (hopefully) ignore any slight abnormalities.

    Also, since many houses have aluminum gutter downspouts, would burying a steel container underneath the bottom of that downspout show as a different metal, on the detector?

    Finally, if you were to cache around an underground power line, how would that show up on a metal detector?
    Oltymer likes this.
  19. Oltymer

    Oltymer Monkey++

    Burying a long steel object in parallel with a galvanized water pipe, or cast iron drain pipe would indeed hide it from the newer digital machines, but a good operator using an older analog unit might detect the bigger mass along the galvanized water line, since they were usually only 3/4", cast iron drain lines would cover about anything though. Most operators would write it off as just more steel plumbing underground in either case.

    Not all gutter material is aluminum, steel is mostly encountered. Still, large aluminum will swamp a detector and make it very difficult to differentiate between any aluminum downspout and steel, but not impossible.

    Some detectors are very sensitive to EMI caused by power lines, others can shrug it off, and none of that capability is price based either, as some expensive units are affected as are some cheaper models. Years ago a friend of mine had a top of the line detector that was about useless in the downtown area due to it's wonky state when around all those power lines, while my cheaper machine of a different manufacturer cut right through it with little problem. So depending on a power line to mask is an iffy proposition. Underground power would essentially have the same effect as the above ground lines, and it is dangerous to bury anything around underground lines that is conductive, so I would discourage that.
    natshare likes this.
  20. oil pan 4

    oil pan 4 Monkey+++

    That's good news, I just started welding aluminum so a lot more small aluminum scraps and shavings will end up on the ground.
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