Answer from Victoria Stilwell:
Dogs attack other dogs for a number of reasons but the root of most reactive and aggressive behavior is insecurity and fear. Keenu might be reacting negatively because he feels threatened by social interaction or has had a traumatic experience around other dogs. He could also be protecting you or the space around him which is important for his safety. Whatever the cause, dog to dog aggression is a serious problem.
In a perfect world our dogs would be social and comfortable around all dogs they meet, but this is an unrealistic expectation. Although the behavior is frustrating, try not to punish Keenu if he reacts badly and quickly remove him from the situation by walking him in the opposite direction until he calms down. Punishment will only make him more insecure and shut him down, making learning impossible.
Keenu needs to feel more in control. When nervous dogs are given choices they tend to cope better in different situations. A leash is a canine life preserver and important for safety but a leash also stops a dog’s ability to act naturally. Most dogs would rather put distance between themselves and a perceived threat, but the leash stops them from doing so, causing a defensive reaction. Some dogs that react towards other dogs on leash are much more comfortable when they are in an off leash environment.
From now on all good things should happen to Keenu when he sees another dog approaching. Before introducing another dog, teach Keenu a variety of alternative behaviors and/or games he can play. When he is proficient at these behaviors or games it is time to introduce a calm leashed dog at a distance where he feels comfortable. As the dog walks past, interact with Keenu and allow him to choose the game or behavior he likes. If he reacts negatively at any time, walk him away from the dog to a distance where he feels comfortable and start the process again. The secret to this training is to keep him comfortable and under his stress threshold level. After a time Keenu will become more confident as the approaching dog now signals a game or something fun rather than a threat.
Once Keenu feels more comfortable walking past other dogs, gentle introductions can be made. This is best done with a very calm dog that is good at giving pacification signals that demonstrate low threat. Face-to-face greetings aren’t recommended immediately, but simply experiencing positive things in the other dog’s presence, including walking or activities at a comfortable distance can help build a positive association. Parallel walking, following the calm dog and sniffing the behind before a facial greeting can be beneficial, but this is better done under the supervision of a qualified positive trainer to guide initial interactions. You can find a humane force-free trainer at: www.positively.com
Dog parks are not recommended for dog aggressive dogs or dogs that play too roughly, as they tend to be overwhelming and cause a bad reaction. Dogs, like people, can be overwhelmed being in a crowd and solitary walks or walking with a small group contributes to a much happier dog and safer interactions.
Keep an eye on Keenu’s body language and allow him to choose the dogs he wants to socialize with and the ones he wants to avoid. Some dogs are happier with their own company or the company of just one or two other dogs. Avoid times of high traffic and off leash areas until he is more confident.