FreetwoDtect said:
In looking at SWR's suggestion of coins under a house. The posts of others who found coins detecting the dirt floor basements of old houses, must mean they do sink. After all there was no grass/leaves to decay, wind or rain.
Dirt floor basements are
NOT a controlled environment. A controlled environment
would be an area where there is no foot traffic, or obtrusion that would create overburden. Sorry...try again

Gee now it did fit your criteria, all the houses were above ground.