This ^^^Try tossing in some veggies, then just scoop them up when the snails congregate, this will get you numbers down a bit. Then throw in some assassin snails. Its not foolproof, I dont know of a way that is, but it cant hurt.
How big is your tank? If you don't throw in too many assassins IME they don't go crazy. But your snail problem won't disappear overnight, either.