You CAN teach your dog to not be dog aggressive and to change and think about his own behavior. After training my dog Joey with Kathy, I've seen Joey pause and correct his own behavior when he thinks he's getting overly excited playing with dogs, or he'll glance at me for permission before doing something like launching himself down a cliff to jump in the ocean.
The main problem that Joey and I had to work on, was that Joey's play wrestling at the dog park would turn into dog aggression. This was extremely distressing to me since he's a pit bull, and people would get extra afraid when this would happen. What would happen, is that Joey would wrestle with a dog or a few at the dog park, and then it seems like a switch would flip in his brain, and in a few seconds he would become aggressive toward the other dog - he would be deaf and blind to anyone trying to get him to stop. Sometimes he would fixate on a specific dog and hound that dog, so I'd have to chase Joey down and leash him.
It was a dilemma because Joey loves the company of other dogs and playing with other dogs, and I wanted him to enjoy playing but didn't know how to stop him from switching to aggressive. I tried using treats and we went to classes at the SPCA, which were great, but didn't help us with correcting Joey's dog aggression. If this is happening to you and your dog, then you know the feelings of distress and frustration - you love your dog, but don't want your dog to hurt another dog.
My friend recommended Kathy to me for one-on-one training with Joey to correct his behavior, and it worked! Kathy will train you to clearly show your dog what's correct behavior while interacting with humans and other dogs. You will become your dog's main teacher, so be prepared to take some time everyday to train. Sometimes it would take Joey 1 day to change a behavior, and sometimes longer. Joey and I met with Kathy for 3 to 4 one-hour sessions per month for about two months, and Joey and I would practice what we learned with Kathy between sessions. It took some time and yes, money, but now I'm so happy watching Joey play wrestle until he's huffing and puffing on the ground and just wants to go to sleep.
Kathy is patient, realistic, and supportive. She's professional and will not waste valuable training time, which I appreciated because it was a big deal to pay for dog training on top of other expenses. If anything, she'd wait until the training session came to a good closing point before ending it. She evaluated Joey first to learn his personality, and then decided what approach to take with him. She never forced me to try anything with Joey that I wasn't comfortable with, and she supported all of her training methods with sound reasoning when I asked her questions. Joey will always be a work-in-progress, but we're done training with Kathy for now. I feel like I can still email or call her if a question pops up.
Kathy leads pack walks, too, so now Joey goes out with her pack 2 to 3 times a week if I know that I can't take him out that day. I come home from work and he's happy, calm, and is ready to snuggle down for the evening. I fully trust Kathy with Joey because I know that she knows how to keep him in line while still giving the pack of dogs the freedom to have a satisfying time and to burn-off energy.