In The Shawshank Redemption, Andy spent years carving a tunnel from his cell to the sewers which was hidden behind posters of various pin-ups.
This question: How was Andy Dufresne able to dig the tunnel for many years without being discovered? - covers why no one ever looked behind the poster.
However, if he was ever transferred to another cell or another prison, his ruse would be instantly discovered. How did he know this wouldn't happen? Or was he just willing to take the risk?