Critter-hunter, the admonition to simply dig lower conductors, is only a VERY small part of the formula, for finding gold coins. Because actually, if the subject is limited to USA gold coins, the $5 and up denominations are actually fairly high conductors. The $5 for instance (which is the most commonly found denomination mind you) reads about 48/49-ish on the whites scale. That's above the beefiest square tabs, and about where corroded zinc pennies would bounce. Hardly a "low conductor". And $10s and $20s read higher yet. Only the $2.50 and $1 denominations would read at tab or nickel-ish.
But aside from this, the much bigger factor is WHERE a person hunts. I mean, you can lower your disc. down to accept all the way down to foil, and go knock yourself silly in junky blighted urban parks all you want. And you will probably never find a gold coin. You will simply dig foil and tabs till your arms fall off. So the much bigger factor in finding a gold coin, is not to simply lower your disc, but is to hunt where their will more likely be gold coins, to begin with. Old town urban demolitions (like sidewalk tearouts in old-town districts), where there is simply no tabs or foil (d/t the locations were "capped") is a good start. Basically anywhere that seated coins or very early barbers are forthcoming in good quantities, is the place to be. And yes, once "there", then sure, don't crank the disc. up to where you're even knocking out zincs.