There are a number of reasons why a dog behaves aggressively towards other dogs. Part of the trick to treating it successfully is to look at the underlying reasons.
Certain breeds are predisposed towards being more feisty with other dogs. Many of the terrier breeds (no, I’m not “breedist” so please don’t send me a bunch of comments telling me why your terrier is completely sweet, I know they are, but they are bred to be a bit feistier) are bred not to back down in the face of a challenge. This can prove daunting if they feel challenged by another dog. Small dogs can show aggressive tendencies as well as the big guys, sometimes worse, though owners sometimes tolerate it more because of their size. Though aggression does not run along breed lines, there are individuals from a variety of breeds that show these tendencies. I have for instance worked with quite a few Labrador Retrievers lately that are showing these traits. It all depends on the individual.
One thing to ask yourself, is whether or not the dog is only aggressive towards other dogs when on a leash or behind a fence? Or if they show the same tendencies when off leash running loose with other dogs. Many owners are very surprised to learn that the dog they thought hated other dogs, did better off the leash. That does NOT mean to go test these dogs off the leash, but behaviorally it does make sense.
First of all, when the dog is on a leash (or tied back or behind a fence or window) it creates barrier frustration. The dog wants to interact with another dog (or human for that matter) but is constantly frustrated in that effort. The frustration level builds and contributes stress hormones into the dogs system. These add up to creating aggressive behaviors, which are then sometimes unwittingly reinforced by the owner. Think of how an impatient person behaves when they’re late someplace important and have to stop at a red light. The frustration builds and the stress hormones increase, changing their behavior oftentimes. This is an example of how it might feel to a dog.
Second, when on a leash, a dogs body posturing is somewhat limited. If the owner has tightened up significantly on the leash, the dog is forced, by virtue of the collar being snug, into a higher stance. That stance may then be seen by the other dog as a challenge and that dogs may react differently then they would have had they both been off leash. Also, the fact that a dog knows he’s on a leash and cannot therefore escape, creates a somewhat “I have to be macho and bluff my way out of this one” type attitude.
And third is what I like to call the “hold me back” principle. We sometimes see this in humans. An unsure person may try to pull a bluff. “I would be able to beat you up if HE wasn’t holding me back” (even though they know full well that if they weren’t held back by someone they would not be so daring).
Also, many owners add to this type of aggressive behavior when they cue the dog that there’s something wrong. They walk the dog down the street and notice a dog coming. Because they are either scared a fight will ensue, or worried about being embarrassed by their dogs behavior, they tighten up the leash significantly (sometimes wrapping it around their wrist). Some owners will grow even more tense and begin to panic (changing breathing patterns as well). The dog sees his owner suddenly appear tense and is immediately on the lookout. Sometimes this even causes an adrenaline dump for the dog. This makes an already unsure situation, grow worse.
These are just some of the contributing factors when dealing with on leash dog aggression. We will in the future give some tips on how to deal with this behavior concern!