The first incident was at our obedience class. He is doing very well in class but spends much of the hour --when he isn't focused on a treat--trying to go visit the other dogs. This seems to be friendly and playful but results in me having to restrain him for a good part of the class. After our last class I was speaking to the instructor and another owner. Our dogs were casually sniffing each other and being quite friendly when my dog suddenly turned aggressive. We separated the dogs, which relaxed my dog. My instructor expressed concern, as did I, as this was the first time I had seen this behavior. I have spent a lot of time at an off leash dog park where my dog plays and interacts with multiple dogs. This makes me wonder if the controlled class setting upsets or threatens him in some way. He also has a regular "playmate." This interaction typically takes place at the other dog's home. In both cases the play is very friendly in which he seems to take a submissive rather than an aggressive role.

The most recent incident occurred today. A friend brought her dog over to play. The two dogs had met before--but on neutral territory--and were very friendly. Within 2 minutes of entering my home, my dog was attacking her dog. We promptly took the dogs outside hoping that my dog would be less territorial. The end result was a gash over the other dog's eye. I am hoping that I can change this behavior before it becomes too ingrained within my dog. What should I do?

A: Your dog is beginning to mature. It's not at all unusual for puppies to be able to play with strange dogs, but then turn too serious about it as they mature. It's time to stop letting him interact in this manner with strange dogs, and hope that the past experiences have not caused any permanent damage in his ability to work with you and leave the other dogs alone.

Obedience class is the ideal place to work on this. Don't let him sniff around at the other dogs. Pay attention to what is going on with him at all times. Direct his attention back to you immediately when he shows too much interest in another dog, by giving him something active to do for you. Keep him busy in class.

If you want him to have playtimes with another dog, look for a compatible spayed female of about his same size whose owner has the same goals as you. Be very careful about these encounters, because every dog fight your dog experiences creates the risk that he will be even worse in the future. He could get so bad that you couldn't even train him to obey you in the presence of other dogs, because all he would want to do is attack. It also puts the other dog's temperament at risk, no matter which dog wins. Of course the dogs can be badly injured, and people can be hurt breaking up the fight.

Don't just restrain your dog in obedience class, because a tight leash and nothing else to hold his attention can cause him to actually become even more aggressive toward other dogs. Give him work to do. Use the time for training, and to learn to hold him in a working attitude for a full hour. It's a wonderful skill for you, and it will help you continue to be able to work with him in public.

I would discontinue the dog park activities. I really think taking him there anymore would just be asking for trouble, and unfair to the other dog owners. There's nothing wrong with a dog who can't go to a dog park and mix it up like a puppy with strange dogs. In fact, that's normal for many breeds.