I have thought for a long time about resorting to pen and paper, aka foolscap, instead of typing. Not only is it slower but it means that I sometimes keep my missives shorter. I know realize that most US elementary school students will not understand cursive so that becomes my secret code. No invisible ink is required, Just my trusty hotel-provided fountain pen.
One other problem is that I can't post on Insiders by this method. Not yet, that is.