Initially the snails may "infest", they are harmless, actually helpful. If you do several small PWC's and keep nutrient levels in check then their food source will diminish. If you have the room get clown loaches, they will keep the snails almost non-existant, as long as you don't overfeed them with sinking wafers or flake. Another option is to wilt a piece of lettuce and sink it to the bottom, with a rock say, over night. In the morning discard it with all the attached snails. Another possibility is hygroponically grown aquatic plants. They are sold in pet stores in the "test tubes". They are usually marked "snail-free". Be careful though, most are not true aquatics. Also it is typical for them to drop leaves to almost bare when submerged. After a few days the leaves will grow back. Why is this? Got me by the sack.

some people treat their plants with potassium permagante to kill snails, some use salt, and some use alum. i haven't done either....b/c i haven't gotten any new plants! so, i apologize for not being able to tell you exactly how.