Of your choices, go with Dunbar. He's a veterinarian and an animal behaviorist. Cesar Millan is a TV personality with very little understanding of dog behavior (the "alpha" thing he pushes has been disproved by wolf researchers) and no actual qualifications. All legit behaviorists find his methods ridiculous. Koehler's methods are outdated and cruel.
A good trainer on YouTube is kikopup. A couple more good behaviorists/trainers (with great books) are Patricia McConnell and Jean Donaldson.
Also, keep in mind that zoos successfully train huge, dangerous animals like bears, tigers, and rhinos using positive reinforcement. Believe me, it'll work on your dog.
A good trainer on YouTube is kikopup. A couple more good behaviorists/trainers (with great books) are Patricia McConnell and Jean Donaldson.
Also, keep in mind that zoos successfully train huge, dangerous animals like bears, tigers, and rhinos using positive reinforcement. Believe me, it'll work on your dog.