Textbook Highlighter

I'd like to be able to highlight my textbooks, but my school reuses them. The Textbook Highlighter would work like those Disappearing Ink pens that expire after 48 hours. The ink in the highlighter would disappear in your choice of 6 months, 3 months, or 2 months. It could be combined with the Ballpoint Highlighter (see link) to keep oxygen out so it keeps until you use it.

Another possibility is that the ink starts to expire in the highlighter (you buy it at the beginning of the year, and when you highlight something, it lasts a certain amount of time until the end of the year.