Like I said on Mogs, I think the rat potion is a great idea but it could be a bugger to implement because of needing a variable player collision cylinder.
Not sure about the watcher idea, it follows a similar line of my previous thinking "I wish AI guards would send something to the chat area when under attack". If guards are placing a watcher & then not staying with it, then no point placing it there.
The keyhole thing has been suggested before, & although good, would be hard to implement.