I think you missed the point of my slightly tongue in cheek post.
My point was if all the drugs, mobiles etc were going undetected , how would you even know there were any? They aren't. Most thing are detected was my point. It's very hard to get things in and out of prison unless there is an element of co-operation (which there often is) and you can never have 1005 sucess rate because people are devious obvously.
I thought the quesiton was so banal to be honest that I certianly wasn't going to dignify it with an answer attempting to explain things to joeluke, there really isn't any point.