protecting personal items

You don't. That is where a room safe becomes important or you reduce the amount of important stuff. I do have a little neck thing that is waterproof and holds a credit card and some cash. My swim trunks are more like walking shorts with a couple of zipper pockets. Have used a heavy ziplock bag to hold some items. It is a great challenge when you have few clothes.

http://www.magellans.com/store/Packing_Organizers___AccessoriesSV102

Sandy, You could also use One of These. There are two models in different sizes, and they'll even fit a small P&S Camera. I always pack one of these along, but haven't had the occasion to try it yet. Happy travels!

I have a waterproof waistpack that I use when I am by myself at the beach. It works quite well. If the hotel has a safe, I leave most of my stuff there. The one I have is similar to the one in Ken's post. I used to have one like the one in Michael's post. That kind works fine when splashing in the water but not as good if you actually want to swim.

We never leave these valuables at the hotel. In the past, we just haven't gone into the sea at the same time...when one of us wanted to cool off/take a swim, the other just stayed with the goods. I would never leave a wallet/money belt/neck pouch/camera/whatever alone at the beach, even if it's buried in towels or otherwise hidden from easy view.

Use the safe in the hotel, it's safer there than at the beach.

Safe in hotel other than some spending money that goes in swimsuit pocket.

Either at the safe at the hotel, or take shifts for swimming. Sucky, but it's the only way.