One of my boxers had this habit and he had severe allergy problems. By time they got the allergies under control we had to treat his paws for yeast. Apparently because they were always wet from him chewing he got yeast infections on them that were very difficult to get rid of. I was finally told to use a spray bottle with water and vinegar in it. This would dry up the yeast and keep him from chewing. My new puppy, (16 months) had shown signs of allergies early on and I started him on Vitacaps liquid with Biotin in his food. He was doing great until I ran out a few weeks ago. He has not started chewing his feet also. Good luck.
CJ
CJ