What happens next?

How to build a dog barrier for your vehicle
Measure your vehicle's interior.
The size of your dog barrier will depend on the floor-to-ceiling and wall-to-wall lengths of your vehicle's trunk area. If your vehicle has collapsible back seats, you have the choice of placing the barrier just behind the front seats.
In this case, run a tape measure from the floor just behind the front seats up to the ceiling. Otherwise, just measure the floor-to-ceiling height of the trunk area behind the back seats.