I also do not recommend pushing an already aggravated dog especially a dog with high defense drives. Forget showing him the 'alpha smalpha' thing (which is way over rated in my book) ,,you will, as ones have pointed out,,get bit and probably get bit good, if you push issues with him.
I also am all for finding a behaviorist, someone who is gsd savvy would be wonderful
) that can come in and observe what's going on with you and this dog.
I respectfully disagree with puppymomma's first paragraph in the above post, I don't think you realize the result of what your suggesting to someone who has a GSD who could do some serious damage if he decided to get physically defensive.
I have gsd's for 30 years, am lines, german lines, czech lines,,never once did one ever growl or try to bite me. It's about mutual respect, being fair and consistent.
Good luck with your dog, your best approach is someone who can see first hand exactly what is going on .
diane