About 20 years ago, I lived in Germany near a small battlefield. I had a small book written about the fight, so I tried to locate the main battle area and check it out with my detector. I found what I thought was the correct spot and started searching. After 30 minutes and not even finding a button, I was ready to go home and rethink my search.
However, before I left, on a whim, I stuck my detector inside the trunk of an old tree that had been cut down. I got a tone and brushed away the dirt and pulled out this: