Ru has a Snoozer Console Car Seat that I got so he could be close enough to touch me in the car without actually riding on my lap. Bucking him in the back seat inevitably resulted in nonstop screaming, which was more distracting than having him sleeping in my lap, but this is a wonderful compromise. The thing buckles down on top of the arm rest between the front seats, and has a tether to attach to his harness. I'm still waiting for the Center for Pet Safety to test how well dog car seats...
