Your dog is likely dog aggressive (DA). It could have been triggered by being attacked by another dog, but most of the time, DA is genetic. A dog is born DA or not. Nothing a person does or does not do controls a genetic tendency to DA.
DA does NOT make a dog bad. DA does not make a dog dangerous to humans. DA and other types of aggression are entirely separate.
My old GSD mix was severely DA. He loved all people, never even growled at a person, but he wanted kill every dog he saw. He jumped through a glass window to kill another dog, and wasn't even slowed down by the glass sticking out of his nose and eye socket. One of the first times I walked him, he dislocated my shoulder to get at another dog.
You can, with much work and patience, keep Dutch from acting like a jerk around other dogs. You can, with much effort and dedication, train him to behave reasonably. You cannot "cure" DA. Nothing you will do will make him like other dogs. There may be dogs he does like. Most dogs aren't as DA as my old dog. But, don't ever think for a second that Dutch is going to be safe at a dog park or around other dogs without a leash on. You could end up killing someone else's dog and then Dutch will be put to sleep.
I would recommend a behaviorist. A POSITIVE behaviorist. No "balanced" or "traditional" people. If they use a choke chain or a shock collar, run away. I trained my old dog using counter condition and desensitization techniques and treats, no prong collar, no choke chain, no leash pops, no alpha rolls, no "tsst" sounds. It took about a year. But the remaining 11 years of his life were great. Now that he's gone, I treasure that.
DA does NOT make a dog bad. DA does not make a dog dangerous to humans. DA and other types of aggression are entirely separate.
My old GSD mix was severely DA. He loved all people, never even growled at a person, but he wanted kill every dog he saw. He jumped through a glass window to kill another dog, and wasn't even slowed down by the glass sticking out of his nose and eye socket. One of the first times I walked him, he dislocated my shoulder to get at another dog.
You can, with much work and patience, keep Dutch from acting like a jerk around other dogs. You can, with much effort and dedication, train him to behave reasonably. You cannot "cure" DA. Nothing you will do will make him like other dogs. There may be dogs he does like. Most dogs aren't as DA as my old dog. But, don't ever think for a second that Dutch is going to be safe at a dog park or around other dogs without a leash on. You could end up killing someone else's dog and then Dutch will be put to sleep.
I would recommend a behaviorist. A POSITIVE behaviorist. No "balanced" or "traditional" people. If they use a choke chain or a shock collar, run away. I trained my old dog using counter condition and desensitization techniques and treats, no prong collar, no choke chain, no leash pops, no alpha rolls, no "tsst" sounds. It took about a year. But the remaining 11 years of his life were great. Now that he's gone, I treasure that.