For those who don't know, to looc a chest you must place a sign above it and type "Lock" on it. But if you want to have chests ontop of eachother and lock them, you cant. So the suggestion is, you can lock chests from the front instead of the top, or both.
If it were both, the system would have to prioritize top or directly on in order to prevent double locking. I personally think it is fine as is, you trade one convenience for another.
How about doing them like message Chests and using a Book and Quill something like this? http://empireminecraft.com/wiki/message-sign/ Instead of charging for Locking it, you could be charged to add and remove names. The person who paid for the original Lock would probably have to be the only person who could edit the Book or remove it from the Chest.
I had the same suggestion, but no1 reacts, cool that you did the same suggestion, so ill quote mine here I like this idea, yeah, but... I will miss the last stack to complete a DC