As an owner of three large breed dogs, I think exercise is of utmost importance, if nothing but to socialise them. If you can try to go o an off lead park, where he can tell you how much is enough. This will also stimulate him so that he doesn't become bored and destructive. I don't have a problem with on lead walks, depending how old the pup is....I wouldn't be walking a 12weeker out and about....I think it is ok once they are about 6 months and have some muscle tone. If you are worried about straining his joints, think more about his weight....I was once " told keep them skinnny but keep them growing", this way there will be no extra strain on his bones...I have had great success doing this with my labs, whereas some people have fat pups and hip/elbow probs!
Best of luck, hope he goes well in the show ring!
