From Jay: As for tank cracks, I have not seen that myself, but it is rare that I let a zoo run for many years. The tank walls are configured to use the deteriorated and broken plexiglass images if they become deteriorated or broken, but I do not know when they would become deteriorated or broken. There might be different logic for tanks, and may even be a mistake in ZT for them to become deteriorated or broken. For land exhibit fences, there are settings to determine how fast they become deteriorated and broken. But stronger animals can make the fences deteriorate or break sooner. And stronger animals might not attempt to go through fences if they are happy. It is possible tank animals work the same way, but I do not know.