My grandparents' cat (a giant orange tiger named "Fluffy") used to patrol their neighborhood attacking dogs. After he ripped up a number of dogs, slashed their noses and rode 'em down the street like a bronco-buster, the complaints got a bit more serious, and the old folks had to tie him up on a length of rope whenever they let him out, just to keep peace with the neighbors. He wasn't aggressive with people, but he didn't tolerate dogs, and back in the early 60's, lots people in small towns used to let their dogs run free. It was kind of sad seeing Fluffy snubbed up at the end of his rope trying to attack a passing dog. I don't know if Fluffy would have challenged a bear, but he never backed down from any dogs that wandered into "his" neighborhood. No dog that had tangled with him ever wandered within range of his rope run, to my knowledge, although once in a while a newbie would wander into "harrass" the cat and learn a painful lesson.