Story is getting around. Third post I have seen relating to it. Amazing. Considering that there isn't a detector that I have ever heard of that will detect more than about 10" I can't imagine anyone diging that deep for a target.
I suppose, as may be the case in my yard, where there might be some major stuff burried in a cluster, like where my brothers burried some old bicycles and a couple of push mowers and other junk, you might detect some stuff deeper.
One brother had dug a hole very deep. Just for the fun of it. He was in high school at the time and decided he was going out to the yard and dig. Like we used to do when we were kids. My parents were out of town and he didn't want to go to school that day. My other brother came home and couldn't find him. looking around, he found him in the yard in a hole about 7 or 8 feet deep, as I understand. I was away at school at the time so I don't know how deep and all. The story was that the older brother had to get a ladder to rescue him.
Anyway, the hole sat for a while until he got the same motivation to fill it, that made him dig it. However, due to erosion and settling etc., there wasn't enough dirt to completely fill it in. So, my two brothers decided to do some cleaning in the shed and garage. They filled the hole and topped it off and leveled it so that we could have a new shed built in that corner of the yard. They poured a concrete pad over much of it and built a little stick built building on it.
I went out a few weeks ago and detected in the area and I get one solid signal all over. I don't even bother to dig there, knowing what I mgiht get into.
I don't know how deep the top of the junk really is. Maybe they only topped it with 10 or 12"

I wonder how deep a detector, even the best of them would detect a Schwinn or two, or three, piled on top of eachother.
I really don't think you would have much luck with gold at any real depth like that. Unless it is a nugget the size of a Buick or something.