In my gardening, I've found lots of debris too. The one I recall offhand is one of those hanging planters, made of wire, that was originally filled with moss. So all that was left were lots of bits of rusted wire, many which made me check on my latest tetanus shot. Why it was found about 6 inches below the soil and on a rocky hilltop (where the dirt is at best 8 inches deep before hitting solid rock) is beyond anyone's guess.