I can't think of a better detector for this than the Mk-1, its tones and meter can't be beat. The only way to go hunting for the old deep stuff-check every signal.
I remember hunting Pleasant Hill, La. for Civil War Relics with a D-Tex 5.5kHz detector in TR at very low iron. I'd locate in VLF
then switch to TR to check the signals, and hear nothing. So I started digging every deep signal, in VLF [and beyond
the reach of my TR disc circuit.] I started finding .58 caliber mini balls, buttons, and some trash. That depth today would not be
a challenge for even a modestly priced detector. The biggest problem with TR's is ground minerals masking the target. You
have the complete size of the loop seeing ground minerals and pulling the circuit negative, and a very small signal of the target
competing with it trying to pull it positive, giving you a response. This is where the motion circuit gives you added depth & performance, but it has some characteristics that are different you have to account for. Example, the bottlecap is easily handled by TR's, but can give some motion circuits fits.
Iron can mask, but not always. With my CZ, if I set it to iron reject, I'm guaranteed to get false signals from iron in the coin notches-yet if I accept
iron its identified correctly, and I can hear conductive targets mixed in. Any detector I use is set at "0" discriminate, and depending on
size/shape, I dig the targets that read iron and good both-a surprising number turn out to be coins. Here's a little added treat for you; iron makes
a coils field stronger and you may have in instances where it can add depth to your detector. There are simply too many times when you apply
all the logic and still can't figure out why you found something under very adverse conditions. But the opposite-you won't know and be able to
compare-you missed it.
As Ty Brook has always said, if you aren't digging trash you are leaving some treasure behind.