Where paint is not allowed, I use colored duct tape. Not the kind in Home Depot, but from Shurtape or one of the other manufacturers. It is at least as robust as good quality duct tape. It will take any kind of traffic with no wear if you get it down smoothly (best done as a 2-person job). After the race, you can easily peel it off the road. It comes in bright colors and several different widths. It is what I use for course layout when nothing else can be used. I make giant arrows in the road to show direction, and big bars across the road at mile marks. When you pull it up, it leaves no trace.