O.k. My sister lives in Texas and the neighbor feeds and takes care of a bunch of feral cats... She has a garden and mentioned all the cat poop in there and I suggested ground pepper... here's her response... Any other suggestions? Other than the obvious?... she just emailed me and told me they leave dead mice in the yard and driveway too.... they have dogs but doesn't seem like its been a help... Anyway... here's what she said... "Thanks for the tip...we've actually tried black pepper, cayenne pepper, garlic, citrus, moth balls, borax detergent and spent several hundreds of dollars to replace mulched areas in the front yard with lava rock...nothing has worked...they actually poop right on the rock...and they have also pooped on the roof, which is gross because when it rains it falls on the patio and sidewalks...I've also tried talking to the neighbor, but to no avail."