We set up our group to not allow greetings. We try to keep the energy low. And we make sure each dog receives the space he needs.
One way we make sure everyone knows which dogs need a little more space is by having them wear yellow bandanas. We've seen The Yellow Dog Project come across our Facebook news feed a time or two and thought we'd help further the cause by selecting yellow as our color.
Any dog that needs more space - be it for aggression, excitement, or fearfulness - wears a yellow bandana to let the rest of group to give them a little more space. With the rest of the group being more aware of boundaries, this allows our "yellow dog" owners to focus just a little bit more on themselves.