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!! .