I built mine in The End. The advantages of mine were:
The Ender Dragon and Endermen could kill almost anything that tries to get to my vault.
Intruders will have to tunnel almost into the void to find my vault.
I created a small cavern under ground, with hidden trapdoors and pressure plates surrounding it. These would drop him into the void.
A triple layer of Obsidian was used.
The trapdoors spread six blocks wide.
The way to get through is a group of levers, which are also surrounded by trapdoors. These trapdoors only open if the wrong combination of levers (out of 9) was pulled.
I used bedrock to create the vault, the vault itself hidden by other bricks. There is only one small gap, made of wood, which looks just the same as the bedrock. The levers set it alight.
The right combination of levers temporarily diffuses only five of the trapdoors. This means you need to choose the right combination of trapdoors as well.
Right outside the vault, after the trapdoors, there is another group of levers. These number the alphabet, each lever representing a letter, and the word 'pass' must be written with them. One wrong lever and every trapdoor opens, causing you to fall into the void.
make a bedrock cube. have a command block designed to teleport a single player, the owner, connected to a button. Does this not work?
just realized when the last post was, sorry.
This is what I've been working on today (see post here: http://www.minecraft...0#entry22409195). I can't see a problem with it yet (with regards to security). Only problem is that it requires an op to build it and set up the command blocks.
I couldn't be bothered to read all 98 pages but my idea is if they get it wrong they are forced into a minecart and then half slabs are placed on top so they can't escape by clicking the cart, it move to fast (if done in a circle) to break the slabs and if youlog out and in again you are still in the mincart.
I know this is not the exact goal, but still, i'll post it:
With command blocks, make a security system with /clear and Gamemode 2 swapping, with a warning before the entrance, after that, there is a cube of bedrock with a code lock, when entered correctly, it teleports you inside another cube of bedrock with the vault inside.