I just threw in a couple of Apple Snails in the snake tank and to my unpleasant surprise realized that the snails have operculums that seal up the shell openings.
Guess if I tried aquatic snails, I have to find some that are large enough, reproduce like a bunny rabbit, and don't have trap doors.
My niece had one of those trap door type snails that closed on the leg of her turtle and drowned the poor thing.