good question, and the answer is???
Speak with a professional trainer in your area. Maybe a Schutzhund club or French Ring type trainer and express to them what you want. A GSD is a fine choice but do lots of research before plunking down your hard earned cash!!! Also speak to the trainers about a good dog that maybe has flunked out of the local police department training...
Good luck to you
Did you pet your dog today?
Proud owner of Black rifles and Assault Canines !!!