[QuickSilver]

Definitely get a physical.

However, it is possible that it is a symptom of something more mild and psychological. I was just a reading a book about how animals in zoos often develop obsessive patterns like this - they are called "stereotypies", I believe.

If that's the case, it's likely partly exercise and also boredom. He doesn't just get exercise on walks; he gets to sniff things, mark his territory, meet other dogs, etc.

I would try challenging him mentally, particularly his predatory instincts. Try feeding him his meal in a kong, for instance. Hide treats in boxes and let him "dig" them out. Is there anywhere indoors you can go, maybe take him to a doggy daycare a couple times?