Yeah. . . the trunk.
We have a Citroen Zsara estate and our 3 ride in the boot (trunk) There is a hefty barrier arrangement to stop them from getting over into the main cabin area. If they are on the back seat even strapped in with a proper seat belt harness they go nuts 'cause they wan't to get into the front seats with us.
The chances of someone hitting me from behind. . . minimal. With the dogs on the back seat, the chances of me being distracted by them playfighting, or getting stressed wanting to get up front, almost guaranteed. probably end up with me rearending someone else coz I'm paying more attention to the dogs than on the road.
Best car for safety I ever had was an old Saab 900i. ( this was before I had dogs )I was sat at the bottom of a slip road waiting for traffic to clear when a guy in a new BMW hit me from behind at approx 60mph (he was on his mobile phone coming down the slip road off a dual carriageway).
The Saab had a crease in the left rear wing and the boot lid didn't want to close properly, because the chassis had been bent it was a write off, but it was still very driveable even after a 60mph rearender.
The Beamer on the other hand. . .well the bonnet was about 4 foot shorter and the engine was in the front seat.