Scott-
There are ready-made ribbons of different colors available for this purpose.
With three strand line, you just measure to prescribed distances, twist open the line's lay, insert the ribbon (directions might say to tie it in somehow for better security). The ribbons are marked with the distance in feet for 30 foot intervals up to 300 ft. I think there's a sticker that also de-codes the ribbons vs. distances by color. Retail about $7.50 at West Marine.
You can also do this yourself with colored waterproof pens, but the fadeing due to the sun will force you to repeat the marking at least every other year.
If you have a windlass, a magnetic switch and counter can be rigged to record the distance out. The windlass manufactuers make them for their own equipment, or you can devise your own. Put "windlass counter' in the search engine and see if you can find our discussion of how to build a counter if you're interested.
Joe.
