Fear aggression is one of the more difficult problems to solve. Removal from the situation till they calm down and long for company again is a good way, if anything works. "You can be scared, but you can't act ~that~ way" Reasoning with a panicked mind is harder than an angry one.
Exactly! He's still afraid of strangers, but now he just sits quietly behind us instead of growling at them. He very rarely growls at us now -- maybe a couple of times a year when he's very worked up. Then we drag him up to his room, and he's very quickly repentant. :)