First make sure he doesn't have fleas. The other possibility is dry skin creating a bad itching sensation. This happened to my dog. adding fish oil (available in the vitamin aisle) to his food daily seems to work.

Examine the area at the base of the tail. If you can see or feel dark reddish specks, the dog has fleas. Get it on one of the modern flea remedies. You could try some of the over the counter products or go straight to the vet for the good stuff. If fleas don't seem to be the problem, see the vet. The cone is only an acceptable expedient until you get the dog to the vet. I give my dogs Revolution, but not baths, and their skin and coat do very well.

his anal glands may need to be expressed

i have a dog that has allergies and chews her hair off all the time on her tail and rear...fleas, grass, food allergies, etc...i use an alcohol 20%/ hydrochortozone or benydril spray 80%. the alcohol kills the fleas and the others soothe and kill the pain etc. and when i see her biting, i spray it on...keeps her from chewing...and changed her diet and lots of baths and cream rinse ha

my dogs doing the same

Those are hot spots. He is allergic to something, most likely his food. Dogs don't handle corn and soy very well, and they are usually the largest ingredients in most dog food. Try switching to a lamb and rice dog food and see if that helps or just give him meat for a few weeks. I had a friend that used to get butcher bones for her dogs when they did that. She'd let them chew the meat and marrow off the bones. That is cheaper than buying hamburger for them.

Are you 100% sure there are no fleas, and has she been dewormed recently? If it's not an allergy, these might be explanations.

Your dog MAY have worms. You need to take him to the vet for a very "simple" check-up! If you LOVE your dog, DON'T procrastinate.

In my experience chewing is often an indication of one of two things, either allergies or fleas. Many dogs have fleas and the owner does not know it, or believe that it is possible. Their dog has fleas? NEVER! Use a product designed to stop the fleas. Then spray the house and area where the dog spends much time. Vacuum the house afterwards. I've been told by our vet that chewing on their back or paws seems to be more of an allergic reaction, perhaps food related. Chewing on the butt or legs or base of the tail may be more likely fleas. It might be an allergic reaction to fleas too though. A food based allergic reaction means something in their diet is causing the problem. Try switching their food to a different product that is designed to be good for dogs with food allergies. (I will point out that our dog seems to react to vitamin E and fish products.) When you switch foods, do so over a couple of days, then stick with the food for at least a few weeks. We found that some foods would cause an obvious reaction in only a week. But it can take as much as a few months for things to calm down. Again, by way of example, our dog is clearly sensitive to Vitamin E. But Vitamin E is a fat soluble vitamin. It stays in the dog's body for a period of time as it is gradually broken down. Finally, keep your dog clean. Too many baths will dry out their skin, too few will leave them dirty and itchy. Brushing your dog is a good way to clean them in between baths. Our dog seems to be best with a bath every 7-14 days.