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All dogs are not the same. Dominance is not an individual trait, there are no 'dominant' dogs, it is an ASYMMETRICAL RELATIONSHIP: in a relationship a dog can be stronger or weaker.
I have bad news: there is no aggression scale. Dogs do not go through all these stages before attacking and before biting. The graphics are eye-catching, I know, but they can be really misleading if we want to understand aggression in dogs.
The belly-up posture, with the dog standing still, is described as passive submission. During play, however, it may be the stronger dog that goes belly-up
For many years I have heard trainers repeat that "you must teach the dog not to pull on the leash".
One statement, two mistakes.