Lankeela is right, and has it occurred to you that your dog is not keen on running for no obvious purpose? The GSD is an intelligent breed and likes to do things for a reason, not just because some human thinks it ought to like exercise for exercise sake ! Your individual sounds to be in that category.It wouldn't be alone.Even quite dopey dogs think that way. Everyone seems to think that big fit dogs, like wolfhounds, not only need but love exercise for its own sake. Yes, well take one down the shops and back and it's likely to give you a dirty look of 'What was that for, you mean you had me walk down, wait and come straight back?" LOL Now, give one sight of a hare and you may need a helicopter to keep up and find it again, but it won't think that was exercise, that was purposeful!