On the subject of the question, Uncle Toad, you might try putting some hardware cloth (wire mesh) over your planters, with holes in it just big enough for the plants to poke through. If you don't like the way it looks, you can camouflage it a bit by painting it green or terracotta or whatever would look the best with your planters. Alternately, you could probably put it right on top of the soil instead of over the very top of the planters. You would need to put gravel over the mesh if you had it right on the soil.