Please Clean Up After Your Dog Yard Sign - Coroplast Keep Off Grass No Pooping Dog Yard Sign with Stakes. Economical and durable, our Coroplast Yard Signs are a staple of outdoor advertising. These outdoor Keep Dogs Off Yard Sign full color direct printed graphics are vertically fluted for use with Stakes. Coroplast is typically used for yard, parking, real estate, and election signs. They are waterproof.