Want your content to be unusable by AI, just use a different writing system. There are two such alternative phonemic writing systems for English with Unicode support, Shavian (·𐑖𐑱𐑝𐑾𐑯) and Deseret (𐐔𐐯𐑅𐐨𐑉𐐯𐐻). While Deseret has a cool aesthetic it’s hard to read for any length of time thanks to all the letters being the same height, so between the two I prefer Shavian.

Admittedly it’s kind of weak because if it ever catches on AI will be trained to deal with it. But hay, if it does get popular English spelling will finally be fixed.