You have not said if you intend to work wet sand or dry sand. Yes I know it may seem implicit in the question that you intend to get on the wet sand, d/t you said "salt WATER....", but ...... just clarifying. Because if you are going to work the dry sand, then you can probably just work it with any land program you like (to your ears preference, etc...). And then of course, open up the disc. to accept everything except nails.
But for the wet salt sand, here's a few changes to make sure are in your beach program:
1) edit out everything below about negative 20 (to eliminate iron, d/t nails and iron start at numbers well below zero).
2) edit out the #'s 00 to about 03, as those are your wet salt #'s
3) edit out positive 95, as that is the hot-rock #.
As for #2, some people may argue that a veerrryyy teensy platinum earing or something *could* reach that low (or a signal that's bouncing around in #'s that low, may take periodic bounces into that range, that you would prefer they didn't, lest you have less chance of hearing them). Perhaps. So for that reason you might want to just edit in those #s, and just be prepared for some flutters when moving in to, and out of, the ebbing surf around your coil. You'll eventually learn the momentary flutters and can just ignore them. But if you think you're getting too much confusion, nix out those #'s.
You'll have to run your sens. way down to about 45 to 50-ish, and the pre-amp gain barely on (or perhaps even off) If this still give you false signals that don't repeat, then try the low transmit option (be sure to re-ground balance after choosing this option!)
Other tips: you might get momentary falses when touching the coil bottom to the wet sand (esp. if your sens. is too high). If this happens, either make sure to not rub the coil against the sand in the swing archs, or turn down the sens.