Tail Chasing

Question
I have a 2 year old German Sheperd who is a perfect companion, exercised daily but as got into the habit of chasing and sucking his tail. I have had him to the vets to check for any infections and he is clear.
Have you any suggestions on how to make him stop this?

Answer
He has another year to go to full maturity.  He may be requiring more and more stimulation.  You might reduce it somewhat by neutering him is not already.  You could look into obedience or agility competition, free form dancing, etc.  If you can't find more time to spend with him, look into letting him spend the day at a doggy day care.