in the walls. think about it, its so easy to take off a panel of dry wall, remove a little insulation, and then put it all back, also there is so many nails, wiring and metal connections in your walls.
it would be really labor intensive to search the walls with metal detectors.
also buring them would be a reasonable alternative, ever try to find something on 60 acres of hills and woods? also just think how many thousands of 1'' ball bearings i just happended to "loose" on said 60 acres
and buring them under something that has been there a long time, like an old rusted out car, or a really big rock.
this ones a little drastic, take the largest spade drill you can get, and hollow out the top of a telephone pole, hide your stuff, and plug it up with a wood plug and calk,
an average telephone pole is about 5-6'' in diameter, and you need a 30 foot ladder to reach it. although getting that close to 1000000 volts of power lines is a bit drastic.
heck, pack em in grease and plastic bags, and put em in one of those pelecan cases and sink it into your pond.
i dont think the feds are smart enough to look under rocks for guns