If you are cheap like me you probably don't buy ropes with middle marks or those ropes with different paterns half way.
Its a dilema. Sharpies and other markers might have halogens in them which can weaken climbing rope. We climbers like taking risk but a marker eating my rope isnt one of them. Beal rope marker is available but its over $10 a bottle.
I found one marker, called the Sharpie TEC which is certified halogen free. They go for about $8 a box, which should last you a lifetime. Sell a few of the extras to climbing buddies for $2 each and its practically free.
Ok realistically, plain old sharpies and most other markers probably won't harm your rope. Lots of climbers use them. I am diggin the Sharpie TEC though b/c it also won't damage goretex or other spendy hi-tech fabrics.
Any one else use this pen?