Just always keep in mind that fear-based anything is just that... an animal acting out of fear.
I think its important to keep that in mind, and remember we can't just correct away fear. We can teach behaviors that are incompatible with aggression, or show them other ways to react in stressful/scary situations, but if we really want to change the WHY of those behaviors we have to deal with and eliminate the fear itself.
GSDs- Mulder, Ridley, Vega
GSD on the half shell- Rigel