being dominant and just being aggressive aren't the same thing. Any dog can become aggressive for a number of reasons. fear, poor socialisation etc. german shepherds are up there with rottweilers, pitbulls and staffies. They are headstrong breeds that will become the dominant member of the household given half a chance. These dogs need firm training. otherwise, yes, your dog can turn into a "terror". Make sure your dog knows basic training. When you walk him, don,t let him lead you wherever he wants to go, make him heel and walk where you decide to go. (the pack leader is always in front) make sure he knows his place in the house. i don't know if you let him up the your sofa's etc but i wouldn't advise it. And definately not the bed! Just remember, its your house, your rules, and the dog must live by those rules. Just use your common sense, you should know which behaviours are acceptable and which aren't, and don't put up with any nonsense. good luck!