
Hi Bill,
If youyvet checked and his anal glands are fine it could also be an allergy. An itchy rear end - dragging, excessive licking at the base of the tail and so on are common signs of an allergy. Especially if he also tends to lick his paws I'd guess he's having a mild allergic reaction to something. Food allergies are common, as are allergies to pollen, plants, household chemicals, etc.
Best way to stop it if it's only a habit is by a combination of distraction and reward for stopping the shuffling. As soon as you see him shuffling immediately call him and give him a favourite toy or a small treat and a lot of praise. You should get to the point where you can catch him before he even starts and distract him before his rear end makes contact with the floor. :-)