Licking so much - he licks his fur off

[phoenix_mom]

Has anyone had the problem of a Bichon - or any dog for that matter, that wants to keep licking themselves on their back or tail so much that they virtually lick their fur off?? I have been to the vet (2 of them actually) and they suggested changing dog food, more exercise and one even prescribed tranquilizers. (I had to give him the latter though.) It seems like it gets better and then it goes right back to a "bald butt." I've recently start putting a toddler's onesie on him to make it harder for him to get to that area and he looks really cute in it too. Does anyone else have that problem?