The dog that seems to lick or gnaw obsessively at parts of its own body can, in some cases, progress to inflict significant damage to its skin. Naturally, the first thing to eliminate in such cases is the possibility that the cause is a persistent itch or irritation caused by some form of extrenal parasites or physical ailment. Veterinary examination is required to look for, and if necessary treat such things as flea or tick infestation or allergic skin disease, the latter triggered perhaps by something in the dog's diet or environment (sleeping on straw, rolling on a lawn recently treated with weed killer, etc.). You may think your dog is free of fleas but frequently, somewhere in its coat, just one, single, tiny, lonely flea can cause a troublesome itchy allergic dermatitis. Assuming there are neither fleas nor any other physical cause, what might be the cause of this obsession?
Simple training can usually put matters right. No need for leashes and halters - the key is establishing a solid owner-dog relationship. Basic obedience training is called for with praise and petting being withheld until and unless the dog responds promptly to commands. When the dog self-mutilates with the owner present, it must be distracted immediately - by throwing a ball, a loud clap of hands, a whistle, the rattle of a tin can, then given a command - "Sit," or "Come" - and a rewad of praise and a food tidbit when the dog complies.
It is more difficult if the self-mutilation only tends to occur when the owner is absent. In that case it is necessary to spy unseen upon the dog and distract it by means of a remote training collar. If a dog is self-mutilating because of stress do not emloy the whistle or loud noise if it causes anxiety. Also, if such a sound signal produces no response, it is best to use a positive distraction instead. It cannot be stressed enough that prevention is the best cure.