Here's one discussion
There's a Smart cargo cover referred to in some threads as roller-blind cargo cover which features a cargo net that attaches with hook and eye (Velcro) to form a secure barrier to items sliding from the cargo floor to the area behind the seats. I believe it's also available without the roller blind part, just the cargo net.
There is another product which I believe is what you were describing, but I don't recall the name at this point. It's like blocks with hook and eye (Velcro) fasteners on the bottom that you can use to "outline" an area on the cargo floor to contain items.
Found it. . .