Leash aggression is probably one of the most common behavior issues. Yesterday my husband came home and said "Luke went after a dog today." He'd been on leash at the time and a guy with a very unruly lab came over to say hi. Unfortunately the dog was dragging the guy over to Luke; you know the out of control type? The dog was pulling and panting, straight at Luke. The straight part was the dogs first mistake, rude, rude, rude. Some dogs just have no manners and to display over enthusiasm along with a straight approach is just asking to be disciplined.
Luke is a very mature dog; and because of this has little patience for nonsense, much like most very mature dogs. He gets along very well with most dogs but if he sees that a dog is going to need some fine tuning he is up for the job. There was a lot of noise and the guy realized that he should probably pull his dog away. There was no contact just noise as Luke tried to school this hooligan. I love labs, they are wonderful dogs but they do tend to be a breed that doesn't much care if someone disciplines them. That is good and bad; bad because they can get into quite a bit more trouble because they aren't phased by discipline and don't listen, and good because they aren't traumatized by it.
How many times has your dog gone off on another dog for no reason? No reason that we can see but for your dog there was a reason. When we leash our dogs we immediately take away their freedom of speech so to speak. We humans tend to tighten up on a leash when we see another dog coming. This alone can start the ball rolling. Pulling the dog in close may kick the guarding mode into gear as well as cause anxiety due to loss of mobility. Many times we pull back on our dog which creates a dominant posture on our dog even when they may not be trying to display dominance. It can all be a misunderstanding; one that can be avoided by space and calm.
Space gives us the ability to NOT tense up on the leash and calm gives off a "we don't care about other dogs," vibe to our dogs. If your dog is pretty reliable in displaying leash aggression, then give yourself more space between you and the other dog and owner. Keep upbeat and happy, don't go into panic mode. Much of the leash aggression problems that are out there are caused by the owner doing everything wrong.
One very important factor in leash aggression is to know that your dog is safely secure on their leash. If you are afraid that perhaps your dog will slip their collar then fix it now. Get a collar or better a harness, that your dog will not be able to get out of. Once you know that your dog is not going anywhere; that itself can be a huge relief. Get a pile of yummy treats to bring on walks with you and treat like crazy for good behavior. Even if you are 100 feet or more away from another dog and your dog does not display, treat, treat, treat.
Even with all the work, all the training and behavior modification there may still be times when it happens. Dogs are not robots, they have emotions and they display them. You are not alone, most dogs display leash aggression at some point. It does not mean that you have an aggressive dog; it could mean that you are giving off bad messages which is causing the problem. Or it could mean that a rude dog has approached your dog or simply that your dog did like what another dog had to say.
Space and calm will conquer.