This is not uncommon in this breed and has been considered an obsessive compulsive disorder but it might also be linked to an allergy issue.
Anxiety meds may help
http://petinfo.org/articles/mutilation.shtml
and you might want to test him for allergies or see if he has a thyroid issue triggering this.
Sometimes going to a food that has no grain and no common protein source such as Wellness fish, rabbit, duck or venison (or other brands with similar formulas) will help resolve this.
With the obsessive compulsive leg licking dog I had I found diet change, addition of omega 3&6 fatty acids such as Derm Caps or Fish Oil caps, and increasing the dog's exercise by a good deal, plus redirecting the chewing behavior to an approved chew item such as a smoked bone, stuffed kong etc. helped him a lot.
But back then we didn't know a mood elevating drug might help too and now we do!
Good luck with him!
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