Dog is suddenly aggressive

Without meeting your dog, it's impossible to know for sure. That said, here are some of the most common reasons dogs begin to show aggression toward other dogs:

1. The dog is coming into adolescence. Adolescent dogs are little fur-covered containers of raging hormones. Even if the dog is spayed or neutered, the body--and temperament--is changing. The dog who formerly ran in fright from other dogs might now take the offense. And many dogs who are genetically predisposed to aggression begin showing the signs at this time. Whatever the cause, aggression often manifests between the ages of six months and eighteen months. Intact male dogs are the most likely to show adolescent-onset aggression, particularly toward other intact males.

2. Your dog has not been socialized enough. Even if you have more than one at home, this doesn't guarantee he won't display aggression toward unfamiliar dogs. And because each breed has a specific play approach, a new dog's style may be very different from what your dog is used to. That alien body language could cause confusion--and potential aggression--if he feels threatened.

3. Your dog had a traumatic experience. Let's say your dog loves other dogs, but one day at the park, another dog attacks him. Now your dog may be on the offense when he attends the park, thinking other dogs mean him harm.

4. Something is physically or medically ailing your dog. This is commonly seen in older dogs with conditions such as hip dysplasia or arthritis; these dogs just don't appreciate the body slams of enthusiastic younger pups. But illness or physical issues can strike dogs of any age. If your dog is feeling unwell for whatever reason, aggression may be a symptom. Any time your dog shows sudden-onset aggression, a veterinary checkup is in order.

The best course of action is to address this problem before it worsens, as aggression issues tend to escalate if left untreated. Use the services of a professional trainer who uses positive reinforcement methods. Get a recommendation from someone who has used the trainer before, ask your veterinarian, or check The Association of Pet Dog Trainers' web site (www.apdt.com) to find one in your area.