My friend has a horribly dog aggressive dog (BC/Aussie Cattle Dog X).

We've been working with Nanaboo to try to combat his aggression, and its working well so far.

We take him to a place where dogs have to be leashed (Petco, etc), and have a Gentle Leader on him. My friend has a pocket full of treats (I'm mostly just along to run interference should someone's dog get loose or something). We walk Nani around the store, letting him see other dogs and such. When he starts getting aggressive when he sees a dog, she pulls his head around (hence the GL) and holds out a treat. She makes him sit, lie down, do a trick, anything- As long as he's focusing on HER.

Its working well so far. Nani is learning to focus on her exclusively, and not pay attention to the other dogs.