First thought would be to buy/borrow a metal detector.
This approach only works if you know a bit about your local geology. I tried
using a high end metal detector to find the iron stakes marking out my first
home and to avoid having to pay the surveyor come back out and reflag the
lines for me... Then I discovered the area I lived in was a main source of
during both the revolutionalry and civil wars (during the later, the next
town over was the primary source of cannon!!)
Needless to say, I got "hits" on almost every rock on the property. I never
did find the stakes.
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