I trained a dog that freaked about bicycles, other dogs, cars, kids, and anything that passed him on a walk. He barked and lunged at them. Once he got to them he’d sniff and walk away, but it was scary for whoever he lunged at and embarrassing for his owners. The woman training him before me called him a “reactive” dog and said nothing was working. I decided simple is best, so I trained him to “leave it”.
Every time something would come near I would say “leave it” and stick a treat in his face. If he reacted after I’d keep walking. If he didn’t react he’d get another treat. I paid attention to our surroundings at all times so that I could treat him BEFORE he reacted (that’s the key). I just kept it up so that he knew he should focus on me and he’d get a treat.
Then I started rewarding him only if he looked at me without reacting when I said “leave it”. Then I rewarded him with a treat every other time he focused on me and just a pet and verbal praise the other times (so he wasn’t treat dependent). I walked him 3x a week for 2 weeks.
On our last walk I said “leave it” and we walked past a playground with screaming, running kids, bikes, and other people with dogs. He didn’t even notice them.
Every dog is trainable. You have to figure out their learning style.