Depending on the pup's age and temperament, you may not be seeing protectiveness per se, but anxiety ---some of which he may be picking up from you. It's a kind of "I'll get you before you get me" approach which isn't actually protectiveness and may well backfire down the road. Then too, unless your puppy is older (e.g., 6+ months), most folks, especially sketchy ones, aren't going to be intimidated. By contrast, an adult GSD can intimidate many people just by staring them down. Size matters, so does bearing.
For protection, I would think you'd need a more stable temperament in a trained, adult dog. I understand (don't do this myself) that there's some protection training one can do with puppies (again, depending on age), but that will take time and expertise/experience on the part of the trainer/handler. Do you have such experience or are there nearby trainers who could help you with this? If not, post your location and forum members may be able to make suggestions.
ETA. For now, I'd encourage you to carry some kind of personal protection that's legal where you are (e.g., gun, mace, pepper spray, bear spray, etc.). Depending on his age, I'd focus on teaching the puppy basic obedience (e.g., leash manners, sitting quietly on command, how to behave in public). Note that barking and lunging are not appropriate behaviors if neither of you is being attacked. So, you want to control that, teach him better options, and that you have his back. That, at least, can lay the groundwork for the kind of protectiveness you may be able to achieve later on.
