My wife and I have a marble'ish jacuzzi tub in our master bathroom. It sits in a little niche in the wall, and the top side of the tub is surrounded by rectangular marble pieces up against the dry wall to keep the walls from getting wet. The caulking on the top of them is shriveling up, and one of them is loose because of it. What sort of caulking or adhesive should I use on these to make sure they don't come completely off?