put a stocking or something over the intake, especially good if you have a strainer, or even better cut a large piece of sponge to fit over the pump with a small cavity before the intake to keep any small snails out
Only if they can lay their eggs above the water line. Most of the babies will probably not survive though. I'd have to see your setup. Here's a cool video that may convince you to give them a real home of their own.