Climbing outside is a ton of fun. The wind, the fresh air, the entire atmosphere is part of what makes climbing enjoyable. It's important to protect the environment that climbing is in. Part of being a good steward at our crags is not using excessive tick marks, lines to show where holds are. If you do decide to use a tick mark on a route or boulder problem be responsible and brush them off after you are done for the day. The Access Fund made a great little video of a climber getting a little too zealous with his ticks.