kingskid1611 - I understand there will be a monetary expense, in that case what would be a reliable equipment.
relevenatchair & MiddenMonster - I am positive there is no Access, chamber or hollow, hidden section as we built this new house ( with 3-4inch concerete floor) where an old structure was in place, now there is speculation that some gold may be buried in the ground under it, and want to know what is the best, economical and reliable method to validate at the least.
The "best" method is research .
Only until proven fact (vs speculation) ensures odds you can afford , no digging or demolition.
I understand the desire to recover a possible cache. (!) And how far speculation can be chased....
I found a rainbows end once with good information. It was not pretty. The information was not the fault.
Many leads odds get thinner with more research. Many.
Research through fact finding to prove to yourself that it is worth the effort and expense.Success depends on it.
Equipment varies with recoveries.
Start with your head.
Success is desired for you. Looking at a demolished floor with no recovery.... Is not.
How would you bury gold under a floor?
When kingskid suggests a tunnel in an earlier post ,why would he?
Remember recovery for who ever cached it.
Digging three feet under a corner of the floor from outside the building would be easier. ?
An already (deliberately) low spot like a cellar or storm shelter or?
We can't see the site from here.
Corners are easy to find. Even at night when less eyes are around. What else is?