Just bought a cargo liner from an online vendor who advertises in the back of Popular Science
http://www.weathertech.com/ Turned out to be a thin plastic sheet molded a bit to contain debris. Does have a bit more friction than the hard plastic cargo bed but not enough. What I really wanted was a thick soft rubber liner like the Nissan factory floor mats.
This thing cost $100 plus shipping - way overpriced. A fair price would have been maybe twenty bucks.
If you need something like this, I suggest fitting an old piece of carpet back there.