Some high-energy dogs develop leash-frustration, especially dogs that regularly visit the dog park. These dogs learn that other dogs equal rowdy, unchecked play sessions and have poor self-control. When they spot another dog, they prepare to launch into their normal rowdy behavior, only to find themselves restrained by the leash. Their excitement quickly turns into frustration, which can manifest as leash-reactive behavior.
Other dogs are conflicted about or fearful of other dogs. Dogs respond to threatening situations with one of three responses: fight, flight or freeze. When a dog is on a leash, his option to flee is taken away from him. Trapped by the leash, the dog is forced to walk closer and closer toward the other dog, when he might otherwise have chosen to keep his distance. Feeling threatened, the dog explodes, lunging and barking signaling for the other dog to go away.
In each of these cases, this over the top behavior will often get worse and worse, in the first case because the dog gets more frustrated and there is also a rush of adrenaline. In the second case, it’s because from the dog's perspective, this reactive behavior is very effective because each time he does it, the other dog goes away. He doesn't realize that the other dog probably lives two blocks over and is on the way home. In the dog's mind, his behavior effectively prevented a serious conflict.
So if you do want to allow your dog to meet and greet, make sure that your dog feels comfortable first. Look for signs of discomfort or conflict such as lip licking, averting gaze or turning away, tail tucks or ears pinned or look for signs of aggression such as staring, ears pricked forward, hackles up and tail high and stiff.
If you see none of those signals and you feel as if you want your dog to meet and greet; drop your dogs leash while the dogs are greeting (if you’re in a place that’s safe enough to do this. That way if your dog feels uncomfortable, he can move away when he feels like it.
