Why does a dog turn his rump towards his master instead of facing him?

Answer 1

It is a sign of submission. At first, the dog is showing that he is not a threat to you, and allowing you to be the Alpha, or pack leader. With time, presenting the hind quarters was rewarded with a good back scratch and probably some laughing and mention of the dog's name, so it became habitual. In other words, the dog was always getting a pleasant outcome for presenting the rump, so will continue to do so. Even if now told "no!", the dog is still getting a response, so it's more fun than just sitting there being ignored. The only way to change this behaviour is to ignore the dog completely when this happens, and reward it with praise when it does something you want - sit in front of you and lift a paw, whatever. It won't take long for him to realise that the rules have changed. He'll train himself to do whatever gets him the most attention.