I put bird netting fences around my garden beds that I didn't want them in... I left access to their 'spa' under my lilac bush. They have just recently figured out how to get into one of the beds, after the fencing being there for over 4 months, so it should work for awhile at least. I'm thinking of trying some kind of netting, or maybe chicken wire, on the ground next year; just something to keep them from being able to dig, and that the plants can come up through. I don't use the bark mulch, though; as that would have to be on top of any netting on the ground, I'm sure they wouldn't leave it alone.