That's pretty deep. Well beyond a hobby detector, even on very large objects. Think for most of us, 12 inches is sort of stretching it. Mine will tell me there is something down there past 8 inches, but seldom a steady, readable signal. Not much digging much deeper most of the time anyway. I doubt seriously there exists a $300 machine that can do 3 feet or more. Skeptical about those really expensive machines that make those kind of depth claims. There probably is something, but well beyond our price range.