The only issue with colored duct tape is that it will not adhere on damp pavement. Once it is smoothly down on dry pavement, no amount of water will wash it away. When pulled from either end, it comes up easily.
Jim, I remember the anthrax scare thing, too. A physician was arrested while laying out flour for a hash run. Can you imagine the weirdest of psychos laying out huge arrows on the road from a giant bag of anthrax? To me, this was one of many pieces of evidence that the terrorists were winning their battle with a frightened and slightly hysterical post 9-11 public.
I was detained by two Secret Service officers years ago who stopped me while I was painting a finish line mark for a 5K that was 2 blocks from the White House. They let me go after my story checked out.