Puppies can really be a handful. It takes a tremendous amount of patience, guidance, leadership and training to have the puppy you want now and the adolescent and adult dog you want in a few months. I actually work as a trainer so I hear this complaint often. First, you need to crate train you GSD. When you can not have your eyes on him. he should be in his crate. Supervising your dog and crate training your dog is just the first steps. I would highly recommend you begin a training program with your GSD immediately. The "Place" command, a nice, respectful walk (no pulling, lunging, sniffing or marking on the walk), foundation obedience (sit, down, recall) and threshold compliance (waiting a doors, for food and permission before exiting the crate) training should begin today. There are a lot of videos on YouTube about training dogs. I have one trainer that I highly recommend for his training videos, Sean O'Shea at The Good Dog. If you watch his videos on YouTube on the training I have suggested for your GSD, you will be on your way to becoming the leader of your pack. If you do not lead, your GSD will take that position which can and usually does cause some pretty major problems. What many people do not take into consideration when getting a puppy is the amount of training it takes to have the well behaved, obedient dog that they want. Smaller dogs, like your pug, tend to get away with more unwanted behaviors due to their size. When you have a larger dog, like your GSD, unwanted behaviors are not as easily accepted or overlooked. Advocating for your Pug is your responsibility, allowing your GSD to abuse your Pug is totally unacceptable. The good news is, you can change your GSD's behavior with training, consistency, leadership, structure, rules and accountability. If you have any specific questions I can answer for you, please let me know.