Suzy,.Thanks for the additional information. It is helpful. It sounds to me like Henry is a bit dominant. A tail head up is a sign of dominance and possibly aggression. While you have had him in obedience classes, it was when he was a puppy. As a dog matures, they become more confident and dominant. Typically a dominant dog will start testing their boundaries between 12-24 months. In my personal experience, 18 months seems to be when they test their owners to see if they are more dominant then their owners. This might be refusing to obey a command, or growling when the owner goes to take something away or just refusing to get off the bed. To us, it might not seem that important but to a dog, if they get away with it, the human is seen as less dominant and the dog may think they are the boss.
Once a dog feels they are the boss, you will see them start acting a little different. They might become more protective since the leader protects the rest of their pack.. Often they will bark at other dogs in an attempt to scare them off. In some cases, they will do this if they are scared as well, but his tail position does not indicate a scared dog but more of a dominant dog..To correct this, you need to get him back in obedience classes or at least start daily training sessions with him. This will establish you as the leader again. Each time a dog obeys a command given, it makes them a little more submissive even if they are only doing it for the treat. For treats I suggest hot dog slices or liver slivers as treats. The following site is helpful for teaching you how to train your dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.http://www.schutzhund-training.com/training_theory.html
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below. http://www.pets.ca/articles/article-dog_nilf.htm
Obedience and the NILF will help establish you as the boss and also help the dog listen to you better. That will allow you to call him back when he rushes another dog. As boss it will be your job to protect him and not his to protect you. He should be less confrontational if he is not the boss. It will be helpful if you can find someone with a dog to help you once you have your dog listening to commands consistently. What you will do is have your dog on the leash. You will have your helper off in the distance. Your helper will gradually move their dog a bit closer to you preferably walking past your position in the distance. As long as your dog ignores them, you can give your dog praise and a treat. The second you see him fixate on the other dog or show any other sign of aggression (hair standing up, etc.) give your dog a correction by giving a short tug and a firm low toned "NO". It shouldn't take your dog long to realize you will not tolerate the aggression and that if he ignores the other dog, he gets treats. Once this happens you can repeat the training moving the other dog closer until he is no longer trying to lunge at other dogs. You will need to practice this when you and your dog are walking as well..Another method that some people use is called the Bat method. You can read about that here:
You can also teach him the speak and quiet commands, but he is also being aggressive toward the dogs, so he needs more than just to be taught not to bark. It seems easier to teach the quiet command after the dog has learned the speak command. The following site explains teaching speak and quiet commands.
I hope this information is helpful to you and you are satisfied with my response. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have .