Wrist mount here. First I love the device, which I use in both computer and gauge mode. My only complaint is that I've had a problem or two with the computer not turning off no matter how much I rinse, shake and dry it (out of the mount), especially in very humid conditions. Annoying and a bit of a battery burner, but no issue underwater.
Rinse under running fresh (tap) water, and dry thoroughly. The problem is residual salt on the water contacts (the metal dots between the two buttons) creating a conductive path. You have to get all the salt off.