^ Well having never tried to remove spray chalk myself, I'll have to take your word for it.
It still seems like a good soaking on Sunday would help, but it would probably have to be brushed as well.
What happened when Nenshi did this last time around? Were the volunteers just better/quicker, did the media have better things to worry about, or was there a little controversy too? I honestly can't remember the fallout, but I do remember that is was part of his election morning strategy.