I think the deepest signals Ive gotten 9-12 inches. ?It was until recently that I started noting what I found at what depth, but without going through my records, they are at home, and I am at work now, this is what I have found.
1794 Large Cent - approx. 11 inches.
1917 Mercury dime - approx. 9 inches.
1826D French half Franc - approx 10 inches.
The 1794 Large Cent was found years ago, with a detector that did not have a depth gauge. ?I remember digging the hole, and thinking nothing is 6 inches down, checking the hole, have it still be in there, and thinking nothing is 7 inches down, and having it still be in there. ?This went on a few more times, and there was even one point where I filled the hole back in and walked away and then went back and dug it again.
The mercury dime was odd, because it was obviously well circulated. ?It really weird how a dime that spent that much time in circulation got so deep.
The french coin was also really weird, since it was in a new cemetary where dirt had been trucked in for fill. ?So this coin was laying someone else, and ended up in a new cemetary, 9 inches deep.
Anthony