Recently authorities in Tysons Corner Virginia demanded that marks for a 5K course be covered up or removed. They had never said "no painted marks" or anything, but anyway. I told the race managers to go ahead and cover them up with black paint. This actually preserves the marks pretty well-- sometimes after a few years the only marks you can find are the ones that were protected by black paint.
I've had mixed results with spray chalk-- mostly it lasts for quite a few months. But I recently discovered that salting the roads in winter can practically wipe it out.