I prefer to get the legs into the sand for stability (rather than use any "snow shoe" approach) , but one trick is to always extend the lower legs all the way out before you walk out onto the sand. This keeps the leg locking mechanisms as far from the sand as possible. And of course, never lay the pod down on the sand.

When I was using a 4x5 in wet, windy situations, I had a nylon stuff-bag (such as used to stuff sleeping bags into for backpacking) that I would just slip over the camera and tripod head as I was walking around, etc. They even have a cord to tighten the opening of the bag around the tripod legs.