Club I went to a few weeks ago had pieces of rubber mat about four inches square with a landscaping nail holding them down, they weren't the most visible but worked really well because you could stand right on them, they painted them different colors for the different classes. My club uses rebar with a piece of colored tubing on them. Another club I've shot also used rebar but then slid a piece of one inch PVC with a cap on it painted the appropriate color, whole thing was painted, not just the cap.