In my experience the Garrett Seahunter for about $750.00 is the best underwater machine. You have to learn how to use it and it has some quirks such as needing to be ground zeroed quite often , which can be done by waving it over your watch, but I have seen people find coins three feet deep in cracks with the loop turned sideways, which I always believed was impossible. My understanding was it had to be under the loop, but I have seen it myself. For underwater you get rid of the pole and just wear the detector on a dive belt and keep the loop in your hand that does not have the watch on it. If you start getting too much noise in the headphones run it over your watch and it will go silent again and listen for the slightest sounds if you want to find things really deep.