Somebody should lock the gate

A kangaroo kept getting out of his enclosure at the zoo. Knowing that he could hop high, the zoo officials put up a ten-foot fence. He was out the next morning, just roaming around the zoo. A twenty-foot fence was put up. Again he go out. When the fence was forty feet high, a camel in the next enclosure asked the kangaroo, "How high do you think they'll go?" The kangaroo said, "About a thousand feet, unless somebody locks the gate at night!"