Heh, the park they just built near me has a pretty tall slide, but there's a series of platforms in an enclosed structure you use to ascend it, so you can't just fall off a ladder. Kids are thankfully still kids though, and every now and then some kid climbs the outer structure and gets stuck.

The smaller slides are big tubes, and to discourage kids climbing on top of the tube, they installed these big shield wall things... which make them even more fun to climb.