I saw them in an enclosure some years ago, nice lawn and big sandpit. The Wombat wanted to dig into the grass and they kept stoppping it. They wanted it to dig in the loose sand, which would have collapsed had any wombat been stupid enough to dig in it.
Thanks ZYBen, you totally changed my opinion of this exhibit. I was stunned to see it in December 2007 and thought it was the best Wombat exhibit I had seen in Australia. But you are experienced with Wombat husbandry, I'm not. To my knowledge, Steve Irwin designed this exhibit himself (I think he designed all the zoo's exhibits himself) so it is strange that his life-long experience with Wombats did not result in a better exhibit.
The perfect example of what an exhibit should not be: Purely for the visitor's benefit. Are the Irwins really such advocates for animals? (Under the tyrannical rule of Bindi )