The other day I wrote about decorating scuba equipment in an environmentally sound way.
Reader Marwah, who asked the original question, sent me an update. Apparently permanent markers washed off her fins, but paint markers worked great. There are two things I took from this:
The importance of testing out your paint before you do a lot of fancy artwork. It may wash right off. Permanent markers worked well for my rubbery fins, but didn't stick on Marwah's more smooth, plastic fins (as I guess they are).
Paint markers are a fantastic option that I didn't think of. Sharpie, Art Primo, and many other brands make these oil-based pens, so they should be easy to find at a craft store in any part of the world.