Steve, is your cargo area carpet or vinyl? If carpet, put some sticky-back velcro (the loop side) on the bottom of your cargo liner. It should get a death-grip on the carpeted surface.
The back of the 2nd row of seats is carpet, but the rest of the cargo area is plastic. I've actually tried velcro before, using a couple different industrial grade glues, but the bond gets shot to hell after going from winter to summer. I think it's the summer interior temps that do the most damage. Not a big deal, just something to add to the "to do list." I snapped off one of my rear seatbelt holders (plastic) a couple weeks ago pulling out some large boxes, so I'm trying to figure out how to repair that one first.
I still say you must drive around with studded golf shoes, or at the very least, have a super twitchy foot.