First of all, aggression issues of any sort, cannot and should not be worked through, via correspondence. That said, what I can advise you to do is find an experienced animal behaviorist in your area to work with you & Alex. Get references and call them. Ask the behaviorist how many of these kinds of cases they've worked with and what kind of methods they use. Look for someone who uses positive methods, to set up a program of counter-conditioning. Try to avoid situations where you know your dog will "act out" until you can find someone to teach YOU how to handle this situation. There are many ways to redirect Alex's attention away from the other dogs and get him focused onto you as the most interesting thing around. Besides contacting a behaviorist/trainer, I would recommend looking into buying a ‘Gentle Leader’ which works by controlling his head and body movements while applying gentle pressure to two pressure points on the pets head. The pressure points (one located on his nose, right in front of his eyes, and at the base of his scull) release endorphins to produce a calming effect while reinstating that you are the leader of the pack, and he has nothing to worry about. There is no pain involved and it is NOT a muzzle. For more information, you can talk to a trainer near you. I have found that positive reinforcement training works best because it helps to teach the pet how to act in a calm manner around the stressful situation without breaking the trust bond between you and your pet. It is going to take time, but with daily training at a slow, steady pace, you and Alex will be able to work through this.