Dachshunds frequently suffer from ithcy hind ends and can exacerbate the problem severely by the neurotic nibbling behaviour you allude to, Desdemona. It's a vicious circle, I'm afraid. Once the dog starts, he is unlikely to stop, and the itching only gets worse. Birds sometimes start plucking their feathers out for much the same reason, and the results can be horrifying. I saw an African grey parrot who had rendered himself virtually bald from the neck down due to this habit.