As a note, snails will climb vertical surfaces; we had problems with snails on our porches on the second story when we lived off of Middlefield. David got the organic/non bad-for-environment "snail begone" stuff and sprinkled it around the lettuce beds (their favored target).

Additionally, we had issues with squirrels digging up our lettuce and hiding nuts in our planters. So, keep an eye out.