The Saunders silver satin tubular frame is a very popular choice of dog guard. It is constructed from steel and aluminium and is simple to put together with a quick release for easy removal.
There are four different sizes, and to find the correct size is easy to do - just grab a tape measure and measure the gap between the top of your car seat and the roof as shown in the diagram below. Where the question mark is, is the measurement that you want (in centimetres).