[yorkietalkjilly]

Here are some things you might try.

I would start the Nothing In Life Is Free method right away with the aggressive dog to remind him who is the leader and has absolute right over who eats and who wait, etc. Google the term and read how to institute it on the various sites for free.

When he attacks, instantly place a claw-hand to the neck as you stand over the aggressing dog saying a firm "No" at the same time, perhaps even a scruff shake in the process being careful to not pick the dog up or pull unduly on the under side of the neck from taut skin gathered in your hand as you stand over him will give him a quick reminder that that sort of behavior isn't tolerated. Stand there over him until he relaxes and his ears widen out/go slack, his eyes go soft as his body begins to slump, "give in" to a relaxed state. As soon as you see the first sign that he is letting go of his attempt at aggression by relaxing, turn away from him and go about your business, always watching out of the corner of your eye. If he turns right back to the victim or starts once again to attack the other dog, re-claw, stand over again with a "No", stay there until he relaxes or do the "Alert" response below, if he's only alerting, not re-attacking on the other dog.

Watch for him to alert to the other dog, by straightening his neck up tall, bringing his ears up, slightly forward, round, staring eyes, tail up, "freezing" in place and a tensing of his body attitude. The very instant you see that say a firm "No" and stand up, pointing toward him, keeping constant eye contact. Stand him down. That is stand there with eyes boring into his, pointing at him, unmoving, unflinching until he starts to relax as mentioned in the paragraph above. If he keeps keying in on the other dog, rising slowly up a bit, crouching, walk toward him, eyes engaged and finger pointed. When he sees you starting toward him, he will usually instantly break his "alert" and act nonchalant. Once he does, you immediately release your eyes, turn and go about your business. If he doesn't, you walk over to him and stand there pointing, eye-to-eye until he does give in to your leadership signal that you are calling the shots.

By instantly breaking your tense stand-down when he relaxes and quits alerting, your body attitude and quick release-response start to teach him that that relaxed state is what you want and that will get you off his case ASAP. In time, he should associate "alerting" on another dog with a coming stand-down and instantly police himself and stop alerting to avoid a stand-down. But a dog like this has to be watched closely around the dog he aggresses on to catch his early signs and stand him down before he has time to go into the so-called red zone. This is critical and will take some of your time to watch like you must in order to keep him off that dog's case while he's learning whose job it is to run the pack.

Usually one dog attacks another because the victim is unstable in the pack and is being punished for its aberrant attitude or because the "victim" is trying some dominance itself, sending signals to the aggressor that he/she is trying to become alpha. I would also work with the dog he's been aggressing on to teach that dog, if it is unsure or nervous, some obedience skills and other tricks he can learn, get praise, treats, to get him busy learning and trusting you, feeling better about himself so that he is not so nervous, if that is the reason he's being attacked. If he is another alpha type or aspiring to be, you don't need to build him up any more than he is, but watch him as well for the signs he sends to the aggressive dog that are causing the attacks. Likely another alpha is trying to challenge for pack leader, is putting a paw up high on the other dog, standing up on him, trying to mount, putting his ears back flat or very forward, cocking his tail up high or sending scent/body signals he wants to mount or is making deliberate, direct eye contact and the two will either work it out in time or always fight until one is rehomed. Spaying/neutering both dogs can help is many cases, if they already aren't. Also, being sure the victim dog that might be acting nervous or unsure is healthy is good as illness will sometimes get dogs attacked. A vet visit for that one might be in order, too, to be sure the aggressor isn't picking up on that illness, which to them can represent weakness and a need to be disciplined.

Google Nothing In Life Is Free to read how to learn to use this wonderful method of re-establishing yourself as leader of an alpha-type dog. Training him in obedience will further establish you as his leader, his teacher and raise his level of respect for you, teach him to learn to do what you say without question. Lots of praise and treating when he does a "trick" right will quickly show him he's done the right thing and reward his attention. Always stay positive, keep his lessons fun and short and the praise/treat rewards will start to shape his behavior toward a more acceptable type and that tends to lessen alpha type behavior in many in the process.

I hope some of these things can help.