I often wonder how I became the guy that gets all these red zone cases, including the dangerous dogs.
These cases can be rewarding, but they are not fun. Not one bit. There's tremendous pressure, risk, and liability. Sometimes a dog comes to me after a judge has given it one last chance before euthanasia. The work is physically and mental exhausting because if I lose my focus for one moment, bad things can happen.
Thankfully, no dog or person has ever been hurt during training by any aggressive dog with which I've worked. I do a lot to minimize risk, and experience helps, of course. This experience, I suppose, is why I often hear the question: "Are aggressive dogs always mean, or can they change?"
The answer depends on many factors such as the dog's history and treatment and how deeply the behaviors are ingrained. The trainers' skill matters a lot, but not nearly as much as the dog's owner and his or her ability to lead his or her dog. But the general answer I give is: "Almost every aggressive dog can be helped to a degree. Some can get over it completely."
After years and dozens of dog aggression interventions, I've come to believe that very dogs are inherently mean, and almost all of those got that way by being treated terribly. Dogs get over things much easier and more quickly than humans, but some have been treated so horribly that the residue of such treatment will always have some effect.
In my opinion, most aggressive dogs act that way because they don't know any better. It's sort of their default behavior because they've either been allowed to be that way or have been encouraged. Or they didn't know what else to do. Once they are taught a better way to behave, they stop being aggressive. The solution is intensive socialization in situations that usually trigger their aggression under the guidance of a behavior expert who knows how to discourage aggression and reward positive behavior. Eventually, almost all aggressive dogs begin to change.
The exception is dogs with serious abuse histories. These cases require patience and training which takes into account the dog's psychology. Even these dogs can improve a lot--some get over their aggression completely, but the process is more difficult.
In my career I worked with a dog who had bitten seven people, including children, all above the waist. He was so people aggressive he would fling himself against his kennel to try to get to me. At first we had to hold him on the ground to prevent his attacking passersby. It took months of him living with me 24/7, but eventually he become so friendly that I could take him anywhere without incident. He learned to love children. And he ended up at police dog training academy where only the most talented and stable dogs are chosen. I worked with an abused English bulldog who had attacked a horse, a bull, and one of the children in his home. He improved but not to the point his was safe in public. A single man with no children and dogs adopted him and gave him a loving home. And I worked with a German shepherd who, despite months of my best effort, improved hardly at all.
But with the right training, the vast majority of aggressive dogs can improve significantly or completely.