I use this harness from Pet Edge: PetEdge: Guardian Gear Pawprint Car Harness My dogs ride in the back seat, these clip into the seat belt clips. You should be able to use any harness and hook it to the D rings in the rear. I prefer the 2 step harness, no stress on the trachea. Here it is: PetEdge: Guardian Gear Nylon Two-Step Harnesses
I found a Pet Net online. The person I spoke with says the Small size fits the regular Prius. I just ordered it, but it appears that it will do the trick. SUV Pet Barrier | Hatchbag Inc. Pet Net
I know this is a really old post. But my 1.5 year old labrador retrever is starting to hit his head on the hatch. Do you have a photo of how this worked out?
I don't have one handy, I'll try to remember to shoot one tonight. But it's really not hard to just cut an old chunk of rubberized carpet to fit and the 'hidden' area gives you another 8" or so of depth.