I have been using a Tracker IV for 3 years and I go from dry sand to wet sand to IN THE WATER. What the TIV hates is really shallow water, it will give false signals, chatter, etc. because of the constant variance created by the water hitting it while it's reading the sand. Get the coil totally under water and you'll find some goodies! I keep the little red switch straight up, sensitivity around 10 o'clock and discrimination low. (I dig everything) If the waves are really splashy you run the risk of getting the salt water in your electronics and then you'll get a constant beep. Shut it off, take the batteries out........then that's another whole story.
Happy Hunting