Don’t bury them; they’ll come with metal detectors for that very reason. Best thing to do is camouflage them and hide them vertically up in trees - at least in the PNW it’ll work, dense pines.
Well, there are ways to frustrate those efforts, and remember prepping rule of 3.
One set of guns can be easily taken, it’s doubly difficult with two and a triple threat with three.
One set in your safe, one hidden in space in your home or outbuilding and a third tucked away near a whole lot of scrap metal.
Best places I’ve heard to bury guns is in a junkyard or some place where lots of nails have been strewn. I know of several old houses that burned decades ago which might be a great place to bury them.
Or you can buy a keg of nails and “salt” an area to confuse a metal detector.
Easy enough to fool metal detectors if you pack them correctly, with several layers of pvc pipe as the canister
Preppers have lots of ways of defeating searches, even those using metal detectors. It’s been a cottage industry for decades.
IR will spot them plain as day. Metal/plastic doesn’t have the same heat signature as a living, or dead, tree.