The training club I was at this past weekend uses these BRILLIANT, lightweight, super-modifiable barriers to cordon off areas for reactive dogs. I was asking about them, and they pointed me to a video they had made about how to make them. I thought I'd share it for those of you who teach group classes. Or they're light enough you could even take them out and use them in public areas as well.
http://www.posidog.com/barriers/