Cipher Decoder Wheel

This is the culmination of a few years of ideas, learning CAD, loving puzzles and being an all around nerd. I love the idea of a decoder wheel but I was always a bit dissatisfied with standard code wheels as being unchangeable in their coding, meaning they are relatively simple to decode once you've figured out the substitution. If you and your friend are trading coded messages, all a 3rd party needs is to temporarily gain access to one of your wheels and write down the substitution.