I find that works for a little while, but after a while the rain causes the soil to mix in with the stones, and it's back to square one. Pubs work, but not against snails. And it's possible that the lupin-munchers weren't the snails and slugs at all, but the local mice, for which I have no answer.

My begonias do get vine weevilled, but once they get established they tend to be able to survive the predation. But it's always a race to get the begonias uplifted and indoors before the weevils get too big and hungry!!