They have a hell of a solid butt lol. There is a cartilageous plate there. When they get chased by a dingo they run face first into the burrow and if the dingo is persistent and tries to crawl around them they have been known to kill the dingo by crushing it against the roof of the burrow.

The plate is there so when they go in the burrows the predator can scratch at their bums and not worry them.

Koalas have it too, but for sitting in trees