A small Otter-box or Pelican case buried in the ice at the bottom of the cooler (or in the sand under the cooler) has always worked for me at the beach. Of course, I usually only have water or Gatorade, so the cooler (and contents) are not as likely to be stolen as a cooler full of beer.

This works well in a hotel as well. If we are traveling by car, we'll usually have a cooler for water/soda that we'll bring into the hotel room. Of course, we always just leave the Do Not Disturb sign up as well.