There is a genuine Volvo nylon mesh, folding 'cargo guard' ending at 9.49 pm today (Mon 10th Jan 2011) on ebay. Dirt cheap and brand new.
I have one of these to contain my two dogs. Works a treat, is full height and width, securely attached to body hooks, and fits behind either first or second rows (but not behind 3rd row).
I believe the metal rigid ones don't fold into the roof when not in use and need to be removed and stored.
This is the link:-
http://cgi.ebay.co.uk/ws/eBayISAPI.d...=STRK:MEWAX:IT