Back about 1968, I got a signal at the end of a child's slide. The top medium was sand, with clay under it.I kept on scooping out the sand with a sieve type scoop I had made, and finally got the cent down at something over 14 /16inches.There was a spoon shaped depression in the sand and that coin was resting on top of the clay.Like an idiot, I didn't recheck the distance..So two possibilities exist. One. I kept missing the coin and it went deeper. Two, with the high frequency Fisher, the clay acted as some sort of a reflective antenna and threw the signal up and back at the detector...The distance is so far out of reality, that it has been bugging me for forty years Is # two possible? Cordially NAD..