i read your post , and thought it's not uncommon for dogs of these breeds to toe out in the rear left , but you said rear right leg , then i seen the video , it is his left rear ? he's more extreme than most , but believe me , toeing out in the rear left is very common , he may be worse due to his rear appears weaker than it should be ........ i'd walk him a lot , as much as i could as long as i saw no discomfort , uphill would be excellent ........ i think often pups are overprotected from exercise and it causes them harm because their strength doesn't keep up with their growth .....my observation has been , the stronger you keep your pup , the better they'll turn out .....