[yorkietalkjilly]

Get him vet checked to be sure nothing physical is going on such as causing him pain or soreness or nausea he doesn't know how to handle any other way and get treatment if needed.

Leash him around visitors and use a soft muzzle in close situations where biting might occur until you can locate a good positive reward type trainer that uses behavior modification and can sort of reprogram him. Put some boiled chicken in the tip of the muzzle to get him used to putting his face into it several times and rub it all around on him and then walk away, leaving the muzzle near, before you actually try to put it on him the first few times. The trainer will likely need to visit the home and train him there with you to reprogram you, too.

Read up on the Nothing In Life Is Free method of handling your dog(just Google the term - lots of articles on it), teaching him through this that you are his leader, not his chew toy and the sugarmama days are over. Read some dog training books on positive reward training - the novel length kind that includes the trainer's theories and the why's of training a certain way and start and keep him on a training regimen throughout until he's totally lost all aggression and then keep doing it fairly frequently.

The NILIF method lets him know his free ride is over and now he has to work for everything he gets in order to get things once freely given now. That's okay - this is how canines lived for centuries and they get it. Largely ignore him and make him earn your attention and respect until he's become completely non-aggressive, praising only per the NILIF guidelines.

Believe it or not, dogs respect and accept being treated as followers and often become aggressive due to a lack of leadership, which leaves them with a control roll they are unequipped to handle, making them nervous and insecure. Don't feel bad -most folks have been there in some way or another with a dog at some time in their lives.

Once you start to take gentle, firm but loving control and make him earn your respect and the trainer is working with you both, he will happily start to become a sweeter and loving pet again. But in this case, I would use a professional trainer that comes highly recommended.