The most effective Snail & Slug trap there is! Just bury it so the opening is flush with the ground, put some beer or soapy water in the trap, and you'll catch all the snails and slugs arouond. (Stale beer is fine, they're not fussy!)
If you use soapy water, put some lettuce or cabbage leaves in the trap first, so it's about half full, then surround the leaves with a strong solution of soapy water (biodegradable dishwashing liquid is good for this)
No toxins, no smell, no snails!