Could you make a little one-way snail flap, so that they can get in but not out - and they can't crawl sluggishly out to pass on their poor, poisoned little bodies to hapless snail-eaters?

However, would snails know it was a flap... mmm... might have to play some atractive snail-type music to attract 'em in. Now - what music would snails like to hear, I wonder.