I do like that last suggestion very much- though it would definitely be more effective if your police liason happened to show up at the intersections at the same time- for a few weeks in a row!

Off-topic, but I would like to know if you're having your shop ride on Sunday, my DH and I might be coming up to Phoenix for other reasons and might try to make it. You've made it sound so fun, and there isn't anything posted on the website yet.