Will a stungun stop a animal in an attack?

Depends on the size of the animal and its type. If it's knocked unconscious, obviously. It it remains conscious then it will either be frightened and stunned and stop in its tracks or run away. Since most people don't live near wild carnivores, the most likely animal to be attacking you is a dog. I would suspect that only aatrained attack dog would be likely to ignore even a mild stun.