Puppy fighting older dog, help?

I just got a 4 month rottweiler puppy from a family friend. He nips at my older dog, a 3 year old American Shepherd. The shepherd is calm and trained, so he doesn't fight it unless the little one starts to bite aggressively. The pup has been backing off of it slightly, but yesterday he drew blood on my shepherd's leg. The shepherd had him pinned down and was just snarling at the pup and then released him. The puppy just cried until he was released. Will the puppy grow out of this behavior? It isn't bad but they fight about once every few days. I fear that the puppy will soon outgrow my shepherd and he won't be able to defend himself. Anything I could do to fix this other than getting rid of the pup? I will if it gets to that point but I would prefer to keep him. Should I even be worried, again these dogs have known each other for less than a week. Thanks