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I also have a Frenchie who used to act similar when passing other dogs(not always but most of the time barks and we think it’s because he was trying to be protective maybe but we were not 100% sure if that’s the reason or not). He doesn’t do this much anymore.
When I train him, I do it before he has a meal so he is hungry and more focused on the treats I have. I use freeze dried beef liver treats which are his favourite(he is very picky) .
I also use a “look” command that I taught all my dogs when they were pups, so when I say “look” he looks up at me and I give a treat. That is how I improved his behaviour on walks when I seen a dog or person that he was looking at ready to bark, I said “look” and he did and I praised him and said good boy with a treat.
It’s easy to teach the look command if you have a treat and are at home while teaching that command. I recommend doing it when he is hungry so he is more focused on treats.
For example a way to do it is ;
Have a treat and ask him to come to you and say look and wait for him to look up at you, then start doing this with your hands to your sides with the treats in them which he knows are in your hands and say look and when he looks up(not looking at the treats, only looks up at you) give a treat and praise him. Practice until he knows exactly what you want and then try it on walks when there is no distractions once he does good with that then try doing that when he sees a person or dog.
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