Cheap tricks are cute but really of no use in your situation . A dog will pick up on their owner energy and you dog could be picking up on your concerns and may think he need to protect you. GSD are bred to protect and it sound like your dog is trying to do this. Sometime police stations will have open house on how they train their dogs and people can ask questions at the end. Or maybe you could see if policeman could work with you a little if there are no good dog behaviorists. I hope someone else with more knowledge on how to train dogs with aggression issues will have some ideas for you.
I found this GSD forum and people are having the same issues , I am not sure if it will help you or not. I really hope you can find someone to help you.