I think metal detectors can only tell the strength of the magnetic pull, which means they can't differentiate between a shallow piece of small metal or a large

I think metal detectors can only tell the strength of the magnetic pull, which means they can't differentiate between a shallow piece of small metal or a large piece of deep metal. In other words, salt the surrounding area with lightly buried worthless coins, nuts, bolts or metal scraps and anyone trying to find your loot will give up. Ground-penetrating radar is a different beast, but also has its limitations: https://en.wikipedia.org/wiki/Ground-penetrating_radar#Limitations https://en.wikipedia.org/wiki/Ground-penetrating_radar#Limit...