I just bought Bobby the solvit pet booster seat. Here is a link to it at petco. I bought it at BB&B for $30 much cheaper than petco. but i couldnt find it on their website. It works pretty good, Bobby can still stick his head out the window but I can feel confident that he wont jump out because he is strapped in. The strap hooks to his harness. I put it in the backseat so when I have guests in the car I dont have to move it.
Solvit Deluxe Pet Booster Seat at PETCO