Dog-to-Dog Aggression: Why It Happens and How to Fix It
It’s common for owners to feel embarrassed when their dog shows aggression toward other dogs. As a professional dog trainer, I can tell you that helping with this exact issue makes up a large part of my work.
Why Dogs Become Aggressive Toward Other Dogs
The number one cause — responsible for over 90% of cases — is a lack of proper early socialisation and training.
Think about it: If as a young child you only ever met a couple of people outside your immediate family, were homeschooled, and had very limited social contact until adulthood, how confident would you be in social situations? Dogs are naturally social animals, but they need positive exposure to the world. The more varied, controlled experiences they have early on, the more confident and adaptable they become.
Another common problem I see comes from off-leash puppy classes. Smaller pups are often harassed or intimidated by bigger, bolder ones. For this reason, I run all my puppy classes on-leash. Puppies are allowed brief, supervised interactions to build confidence and good social skills, but everything is carefully controlled.
“The developmental period extending roughly from 3 to 12 weeks of age is the most influential 9 weeks of a puppy’s life.” — Steven Lindsay
When Things Go Wrong
Even when owners do everything right — puppy school, socialisation, etc. — a single bad experience (often at a dog park) can scar a dog for life. Being attacked by another dog can destroy confidence and create lasting fear or aggression.
Dogs that have been traumatised may lose the ability to correctly read other dogs’ body language. They can become fearful or aggressive even when another dog is showing friendly signals. In their mind, the other dog is a threat. If they’re on leash and can’t escape, they often default to “fight” mode. This behaviour becomes self-reinforcing because it makes the “threat” go away.
Important distinction: Most dog-to-dog aggression is defensive (fear-based), not true offensive aggression. You’ll usually see frantic barking rather than calm, calculated behaviour.
How to Rehabilitate Dog Aggression
Strong recommendation: Work with a professional dog trainer experienced in behaviour rehabilitation before attempting this yourself. The following is a general overview.
Step 1: Solid Foundation Your dog needs reliable obedience training first — especially walking nicely on leash, Sit/Stay, and Recall under distraction. I usually recommend at least 3 private lessons to build clear communication and control.
Step 2: Controlled Counter-Conditioning I always start with one-on-one sessions in my controlled training facility (this removes territorial issues). I use one of my own well-socialised dogs as the “helper dog.” Both dogs stay on leash.
The goals in early sessions are:
- Begin counter-conditioning (changing the emotional response)
- Teach that aggression toward other dogs is unacceptable
- Build impulse control
I carefully monitor the dog’s stress levels and always end sessions on a positive note. Progress is gradual — some sessions are short, others longer. Less is more.
Once the dog starts showing relaxed body language and interest in meeting other dogs calmly, we move to small group settings.
Realistic Outcomes
Every dog is different and has genetic limits. Some fearful dogs can become happy and social. Others may never be fully social but can learn to tolerate and function calmly around other dogs. Both outcomes are successes.
With patience, structure, and the right approach, almost any dog can improve significantly.
Key Takeaway: Prevention through early socialisation is always best, but even dogs with established aggression can make excellent progress with professional guidance and consistent training.