My almost-proudest was a dime at 10" (measured) beside a river in the mud - a *&$%# 1996 Roosevelt! I could not believe it and invented some new detecting jargon on the spot. This was in a an area that floods and must have silted in. Grrrrr.
Not too far away I found an Indian Cent that was on the surface - caught on a section of flat shale and the obverse worn to smooth. You just never know.
My deepest was also a pie tin at close to 2 feet. I was hoping there was a cache under it, but nothing. My deepest keeper was probably a wheat at about 10-11 inches.
Iron cannon at over four feet on a fairly stripped beach using a Deepstar P.I. Found another cannon at a later date nearer the low water mark and just couldn't dig it out in time due to tide and sand backfilling the hole. Made shuttering and will have another go at the lowest tides of the year though this year there's around three feet more sand than there was at the time.
found a gigantic RR lock - brass -dated 1864
was down bout 2 feet - 2 other guys with me saw I had arm in hole
up to my elbow and said "give up" "its gotta be a deep piece of iron"
I told them -" i see nice patina green "
they almost sh#t when they saw it come out
Probably 10" to 12" on a stand coin..But I will be honest , Just like Casper said above, I have QUIT on some targets and covered the hole back up because I was scared of hitting a gas line or other utilities...