Something is digging up newly-planted shrubs or other small plants in my garden. It recently dug up 2 1-gal yews and chewed/tore off the roots. Now it is going after a 6-foot magnolia. It seems to be after something in the potting medium, I think. I live in the country (in Kentucky), so there are lots of varmints to suspect--racoons, opossums, groundhogs,etc. I tried sprinkling moth balls around the plants, with no luck. Any ideas on how to stop this critter?