They didn't put a twenty-pound bag of cat litter on board the landing vehicle?

The Opportunity rover on Mars has broken free of the sandtrap on which it has been stuck for over a month. Basically the method of extraction simply involved backing up, gunning it, backing up again, gunning it again, turning the wheels back and forth, gunning it again, turning the wheels again, and so on. For over a month.

I like the tenacious work of those NASA engineers.