Nu Nu the Demon Chihuahua (above) was the hands-down star of the very first episode of Cesar Millan's tv series The Dog Whisperer.
The charming thing about Nu Nu, even at his worst, was not so much that he was meaner'n ratshit, but that for all his aggression he never really tried to injur. He mostly threatened, and might escate to nips, but didn't actually try to hurt anyone
And when he gives up and "accepts" Cesar's presence, even rolling around on mommy's bed, it's really kind of a lovely sequence, and you can even see that this had made him a happier calmer animal overall, no longer threatened by the mere fact of cooperation.
While Nu Nu was alloowed to have his own way, he asserted his complete ownership of and dominance of Tina who catered to his every whim.
She had made him the eternal lap or even head ornament (as shown below), and permitted him the impression that he was allowed to threaten each and every human being that tried to come near She Whom Was His And His Alone.
Without the least threat to Nu Nu, but using only a blocking technique, Cesar very rapidly established his higher social authority. Denied immediate access to Tina, Nu Nu took only a very few minutes to realize he had better placate this interloper.
I've used the blocking technique myself to stop inappropriate behaviors. Hitting a dog, even with the proverbial rolled up newspaper, just reinforces that might makes right.
Or, yelling at the dog to stop barking, from the dog's point of view, is just the two of you barking together. But stand up and block him from getting to his destination, he very quickly figures out he is not in a reward situation.
Some of Cesar's methods are kind of bad. He's all about dominating a pack, when better safer dogs result from a sense of shared responsibility within the pack (packs are vastly more about cooperation than about pecking orders).
He uses a lot of fear-based "obedience to the top dog" control methods which teache dogs in turn to menace whoever is not the top dog. But the blocking technique certainly is an effective short-cut to changing behavior rapidly, annoying the dog until it decides to cooperate rather than punishing or frightening the dog until it knuckles under.