I don't think walking is good exercise for a dog like a GSD, at least not a young healthy one. More frisbee might help.
Regardless of that, if all my dogs needs are taken care of IE food, water, bathroom break, exercise, bonding time and the dog decides to be a little whiney jerk anyway I will mark and punish it (what that is depends on your dog but escalate until effective). Sometimes dogs just act like brats and if that's the case you stop a brat by making being a brat an undesirable option. Condition relaxation in the house too by doing exercises like sitting on the dog or any number of conditioned relaxation exercises.
As I type this I have 22 dogs in this room. They are all relaxed and silent including a 9 week old puppy. I have had most of them in my care for less than 1 week. Take care of their needs, but don't allow the dog to become a demanding jerk.