Exercise to teach a dog to stop going wild at the sight of another dog. Try the "Open Bar" exercise. I will refer to other dogs, but adjust as necessary if it is also people.
For a set period of time (weeks or months, as needed), whenever another dog (person) appears, like clockwork you offer her sweet baby talk or cheery "jolly talk" and a ***SPECIAL*** favorite food ***NEVER GIVEN AT ANOTHER TIME.*** The "bar opening" is contingent only on the presence of other dogs; therefore the bar opens no matter how good or badly Maggie is behaving. Likewise, the "bar" closes the moment the other dog leaves -- you stop the happy talk and stop feeding the treats.
I know it sounds counter-intuitive to give treats to a dog whose behavior is far from angelic. Behaviorists explain that the classical conditioning effect -- creating a strong positive association with other dogs -- is so powerful that it overrides any possible reinforcement of undesirable behavior that may initially occur. The unwanted behavior soon fades in intensity.
Another advantage of the Open Bar technique is that it can be incorporated into training regimens that are easy to set up, such as "street passes." Street passes are also a means of using distance and repetition to desensitize your dog to other dogs. The final goal is for Maggie to be able to walk by a new dog and do well on the first session.
All you need to set up a training session using street passes is the help of a buddy and his dog. Position your buddy and his dog about 50 yards from a place where you can hold your dog on leash, or tie her securely to a lamp post or tree. Ideally, this should be on a street, and you should be about 50 yards from a corner, so your friend can pass through an area of your dog's vision and then disappear.
Your friend and his dog should wait out of sight until you are in position and ready with your treats. At that point he should appear with his dog, strolling across an area within your dog's sight. As soon as he and his dog appear, open the bar and start sweet-talking Maggie as you give her treats. The moment that your buddy and his dog disappear from sight, the bar closes and you stop the treats and affection.
Don't get discouraged if on the first few passes Maggie is too frenzied to care about you and your treats. Patience will pay off. It may take 10, 15 or 25 passes, but how many times in a row can she get totally pissed off? At some point, she will calm down and when she does, she will begin to make the connection with the food appearing and disappearing with the comings and goings of the "treat dog."
Similar sessions can be set up in quiet parks or out-of-the-way places. You and Maggie should stand several feet off a path, as a friend walks by with his dog, also on leash. Both dogs should have an appetite (don't work on this right after the dogs have been fed!) and both handlers should have really yummy treats in hand to keep their dogs' attention on them and to reward the dogs for good behavior.
Your friend and dog should make several passes, until Maggie is able to maintain a sit without lunging. As training progresses, you should be able to gradually reduce the distance necessary for Maggie to react calmly with a "oh, you again" response. You repeat the process as new dogs are introduced into the equation. After going through this exercise several times, Maggie should be able to meet even new dogs calmly.
Remember that the handler is one of the most important components of this team training. Owners who remain calm are better able to pay attention to their dog's body language and to observe what triggers aggression.
If you anticipate or respond to Maggie's aggressive behavior by tightening up on her leash, you reinforce her perception that she should be leery of other dogs. If you get upset when she lunges and barks, your emotions will fuel her tension and aggression. If you continue to punish and reprimand her after she has started to settle down, you will confuse her and make her more stressed because punishment coming more than a couple of seconds after a behavior is too late .. your dog will think she is being punished for being quiet.
You have to be patient. If you stick with this program, the odds are you will be pleased with the results. Of course, I am not there to personally observe Maggie's behavior and there are some dogs that don't respond. You might want to consult with a behaviorist who will be able to observe what she is doing and give you more tips.