get those crayons they make for kids to doodle on the shower wall. Depending on your surface dry erase markers work on some shower surfaces, assuming you have

get those crayons they make for kids to doodle on the shower wall. Depending on your surface dry erase markers work on some shower surfaces, assuming you have one wall that isn't too fogged up or getting wet (hate for your brilliant psuedo code to start running/bleeding/washing away :P )