[uclibc]

Instead of using every n'th letter, how about using a pseudo random number sequence generated by a simple math equation, like the one posted here a few days ago[1], and add that to every letter. With that the data should be shuffled basically beyond recognition though the effort needed to decode has increased even more.

[1] https://news.ycombinator.com/item?id=39091867

[Izkata]

The way I've seen it used in TV shows, there'd be a number somewhere (embedded, or day of month the message was sent, etc) that indicates what page of the book to use.