Have you talked to a vet about this? You have to be careful that this does not become obsessive. My GSD Leather has canine compulsive disorder and will chew herself raw.

This may not be the case since he chews carpet as well, but for some reason dogs might start to lick their legs or paws when they have anal problems. I'm not too sure why yet lol. I'll have to do some more research on that.