Awesome Redstone Code-Lock System!

I was struggling to make an efficient code-lock system with levers that is not too easy to figure out, and I came up with this. It is pretty hard to figure out unless you have the code given to you. It has 9 levers and has 4 correct keys to get to the next section. It has 2 pressure plates but only 1 works. It also has a button inside the secret place if the item on the pressure plate de-spawns. I think this would be good for adventure maps if you used it in the correct way (not like giving the code-lock to them and expecting them to know it). If you have any ways you could make it more efficient or a new idea (terra-forming or redstone) please leave it in the comments!