Hello
I really sympathise with you it is awful to watch them chew and not stop,despite all your efforts. I had a small dog that was contstntly chewing his feet, it was after I got him back from a "home" where he was supposed to be looked after!!!! ( LOng Story!!) anyway after many vet visits, clonicalm was the original answer, and then it returned after a few months skin scapings ( for mites) were next and blood tests. I also had him desexed, which helps in the case of demodectic mite. I have some articles if you are interested, PM me and I can give you my email addy. Other skin allergies, such as food, or dust are possible, and flea allergies. A secondary Bacterial infection skin infection, hormonal disorders or mite infestation are more likely in older animals, but can happen. In the vets final opinion of my dog he stated that the dog had a behaviour problem and the Clonicalm helped, he still chews his feet but not to the stage they are bad its just a nervous thing now. Have you been to the vet ?