For my Lexus 2008 RX350 I wanted a dog barrier with minimal impact -- one that could be attached/removed with no trace of installation, and one that maximized the cargo space in the back end. I found one I'm very happy with.
I found what I was looking for in the Montblanc K9E Headrest Mounted Deluxe Dog Guard. Found it on eBay in the UK for around $100 from a seller that didn't ship to the US, unfortunately. Used my European address and picked it up on a trip later, which isn't a convenient option for most folks, I know. There are probably other ways to get one if this seems like the right product for you.
It's made of steel, powder-coated silver, and attaches to the headrests. It's in three pieces with side "wings" to adjust to fit different size openings. After nine months of use, I tend to forget it's there -- no noise and no significant impact on rear visibility.
Don
Here's the manufactures UK site (from Sweden, originally):
http://www.montblancuk.co.uk/products/dog/k9e.htm
Here are a few photos of the installation in my Lexus:
