If the goal is to make the course more of a challenge then arbitrary OB's and mandos can be agreed upon by the members of a group of players without permanent markings. Improvements like signs, benches, trash cans or general clean up are cheap and benefit all who play the course. PA Disc's idea for alt pins is excellent.
OB lines are usually defined by permanent things like streets, sidewalks, creeks or lakes. Ropes or hay bales (like at the USDGC) are temporary and wouldn't last long if left in place.