Though I agree with the "Don`t try to make him aggressive so early" thing, I totally disagree with the extremists points of view of it making your dog "bad" or never teaching them to be aggressive. First of all, all dogs are aggressive in one way or another. I have raised , trained and been a breeder of dogs of many types and each dog has its own temperament no matter what the type. Some are naturally more aggressive than others. Surprisingly, Pit Terriers are normally timid with humans while Chihuahuas are absolutely aggressive to humans. And if you bought a dog for protection, he or she should be trained to do the job. Not everyone buys dogs for looks. This is why there are "Working" class GS`s and "Show" class. The German Shepherd IS a working class dog and they love it so actually a person buying one who plans to keep him or her locked up, or tied, or in a tiny enclosure is mistreating the dog just as bad or maybe even worse than those who they point their fingers at. The term,"Making a dog more aggressive" is the wrong phrase. You should ask, and what I believe you were trying to ask, was , How do I properly hone my dogs aggression. First you must teach them to STOP when you say STOP. I actually start at a young age by socializing the dog as much as possible but AWAY from my home. At home I am more particular about who I allow to come into contact with him. I frequently socialize him with the mailman, meter readers, etc. but to strangers or others, I avoid contact. Your dog will figure a lot of this out on his own just by being there at home and seeing who comes around and who doesn`t. I also frequently socialize him with any and all children and in fact, I demand the best behavior from him when around children. German Shepherds are natural herders so kids can sometimes be considered a duty to a GS. Be aware of that and command him to be calm and gentle by standing close by and verbally making him aware when he even thinks of getting too excited or pushy with the kids. GS`s are smart. really really smart. So in time they will begin to develop the skills that you have been implying. Push your dog too hard and it will reverse. In other words, treat him poorly and he`ll either become fearful or much too aggressive to be allowed in public. Take your time and treat him like a person. Constantly spend time with him and repeat exercises with him over and over again. NEVER allow him to do anything that could develop into a bad habit. Never try to make him attack someone unless you are a trained pro. Teach him to STOP his aggression before you teach him to direct his aggression towards someone or thing. This takes months and months and months of training so if you don`t have the time to do it right or get it done by a pro then sale him and by a cat. Bad owners make bad dogs.