It was definitely an article by Julie Daniels (http://www.whitemountainagility.com/) I'm pretty sure the title was "Beyond Tolerance - Shaping for Demand".
After helping me out with the teeter at practice, the trainer kindly lent me her last copy of the article - I wish now I had thought to photocopy it at the time. I usually just see that trainer in the winter, so I probably can't get a copy again soon. Maybe one of the agility nuts here will see this and has a copy - there are a few people who have posted or PM'd articles to me before. I think you can also order back issues of Clean Run.