To get some of the harder stuff where I am I ground balance, max sens, and slowly grid or pick a smaller spot to work thoroughly. When deep enough some of the small old copper coins will give a faint or soft high tone and maybe only bounce up and down to say 60ish on the display. When I get that combo I become VERY focused and often do a small rotation or circle around the target to really hear it. I have no idea about the no see ums as I tend not to dig them, it's just too deep and I have gone down to pipes too many times. Alternatively however, as a fellow has already said, deep is often equated with old. It could be old junk, a Chinese cash coin from the 1700's, or a chunk of copper pipe. It's your decision to make whether to dig or not. What often determines whether I want to go the extra mile or not is the sites history. If it has proven to give old relics or coins, or is simply an old occupation site, then those are additional factors that I use to decide to dig or not. Turn of the century school yard with a deep soft high tone, I will dig deeper. 1980's urban grass strips by sidewalks, no, that's shallow clad, knick knacks and jewelry, if in an area with no prior development or historic use.
