To foil the maintenance programmer, you have to understand how he thinks. He has your giant program. He has no time to read it all, much less understand it. He wants to rapidly find the place to make his change, make it and get out and have no unexpected side effects from the change. He views your code through a toilet paper tube. He can only see a tiny piece of your program at a time.

You want to make sure he can never get at the big picture from doing that. You want to make it as hard as possible for him to find the code he is looking for. But even more important, you want to make it as awkward as possible for him to safely ignore anything.

Your code should not look hopelessly unmaintainable, just be that way. Otherwise it stands the risk of being rewritten or refactored.