How to make a secret door in minecraft! (Completely hidden!) - YouTube Enjoy! http://www.reddit.com/r/Minecraft/comments/zbmyr/adventure_mappers_you_may_love_me_for_this_secret/
It works wonderfully in theory, until Sharp joins your server. He practically bathes in redstone dust, and is always looking for more to add to his collection.
The issue with this design is that everyone needs redstone for everything, so people who come by will mine it out. There's an interesting arrow detector that works in vanilla, but I'll leave you to search it up on youtube. Basically, you hooked up redstone ore to a BUD to turn on a jeb door. Nothing difficult.