In the past I have used these Decollate predatory snails in my veggie gardens with great results. Just make sure they are legal for your area. The beer method works great too. Take some cheap beer and cut the cans in half, burry them so the snails can climb in for a swim and collect the dead ones in the morning. The more beer traps you place the more slugs you kill!
Here is one source for the predator snails but there are many places you can buy them.
Decollate Snails (Predatory)-100 - 8220100