My very personal, non-expert, opinion is that it sounds like you don't really have an aggression issue as much as a training issue. He sounds to me like he just gets annoyed with other dogs and when enough is enough he makes it apparent. It also sounds to me more of like a trend with puppies and he doesn't like them in his space.
For when you are around, and he growls at another dog, I would distract him with something, a ball if he's driven, treats and do OB, basically get him accustomed to the idea that another dog in the vacinity means he gets to have fun with you.
Not an expert by any means so maybe someone else will come along with a better idea, but it just doesn't sound like a reall "agggression" issue.
Commander Charly Titan (GSD)-15 Jan 2010