Caches tend to be buried where the owner can keep an eye on them. For example, in the past, women often cached things in flower beds or within sight of their kitchen window.
So if you were hunting a field and didn't know which way the house faced but had a good idea where it stood because of all the glass and coinage in the area. Lots of iron signals. I'm guessing you would have to dig all the iron signals that were at least 10 inches deep or more as a cache would be in a can or a fruit jar with a tin lid?