My Jack Russell doesn't care about food, toys or praise while we are walking, his only focus is squirrels, rabbits, etc... and dogs, with two different reactions. For small animals, he wants to chase it, for dogs he barks and try to reach them at all cost.
He passed through 2 different trainers, I read more than 10 books on dog behavior, I took classes... but nothing, he doesn't change. And by the time is getting old, I'm concerned about his health.
I'm hopeless here, I just accepted the way he is, but maybe you have some advices.

Thank you!