On our small Maine farm we've tried several snail and slug control methods over the years. The most dramatically effective approach for us was a combination of hand picking, habitat control, and the increase of predators (wild birds, toads, and frogs) as a direct result of good land use practices. Beer traps can be effective in a small area, but we were dealing with too large an area. Our bantams have learned to love hunting for both snails and slugs as well as other insects.

Recently we've observed the appearance and dramatic increase of snails in our area. The same combination of controls is effective. We've also added a container of one of the iron-based baits to our options. We'll test that next spring.

I did a quick search and offer three links as starting points:

Clear overview of some control methods

Possible dangers to pets from beer, baits, etc. (Grain of salt warning)

One kind of iron-based bait