Aggression Toward Other Dogs
See this. Two dogs on leashes. One dog barks and lunges, owner yells "NO!" and yanks the leash hard. The dog barks harder. You just made it worse.
Here's the reframe: aggression toward other dogs is usually not aggression. It's the leash.
Drop the leash, let him go — he'll run over, sniff, probably rollover. The dogs can't complete their natural greeting because two humans are holding two leashes between them.
I've seen it thousands of times in our Chicago facilities. Customer brings in a dog "aggressive toward other dogs." Second we let him go in the pen, he's fine — playing with fifty other dogs. The dog was protecting the human.
If the dog is fighting physically with other dogs, that's different. Consult a professional right away. Or call me.