I use a baracuda. A custom Pulse machine waterproof to 200 feet, made by Anchor Electonics of Biloxi. It bites deep and has provide me with four years of great finds. Unaffected by mineralization, it finds targets the other machinesw cant get. I regularly pull rings from 24 plus inches of hard packed sand at the beaches. Mind you it cost two grand to have it made, so you get what ya pay for.