At our local wildlife park, there was one kangaroo who repeatedly managed to leave the enclosure. Therefore, the zookeepers erected a 15 foot fence. The following morning, they found the kangaroo wandering around the zoo – it had escaped again.
This kept occurring until the fence was 80 feet high. In the adjoining enclosure was a tiger who asked the kangaroo, “What height do you say they will stop at?”
“About 150 feet” said the kangaroo, “or until they remember to lock up at night!”