<human>: Can you provide a brief overview of the text?

Background info: We drive a '99 Honda cr-v, and the back seats are usually down. We've had Dax in our family for about 6 months. He turns 3 next month, and he is 62lbs, 1/2 Pointer, 1/2 border collie (we only know this because of the DNA analysis). I spent a whole lot of time with his previous parent, who reported the same things that we have since observed - Dax has a very calm and snuggly personality indoors, but running in giant circles outside and going on long hikes makes him very happy. It is worth noting that the previous parent drove a two-door sedan.

Unless he is outrageously tired, Dax hates to ride in the back. He makes all kinds of stress vocalizations, walks in circles, and has a hard time maintaining his balance. Sometimes if he hasn't had much exercise that day, he'll bark incessantly the whole ride.

BUT if he is super tired (this is usually on the way back home from whatever glorious place we went), he'll lay down in the back almost immediately, and stretch out and completely relax. he'll often fall asleep, even for just a short car ride.

He much prefers to sit "shotgun" and lean against the back of the seat. This is how he rode in a car for the first couple years of his life. To me, the front seat feels like a very dangerous place for him to be. Twice, I have had to brake quickly, and he falls into the feet area, and seems a little jarred. This has completely freaked me out, so I much much prefer him to ride in the back. 

I have tried getting a "down" from him while he is stressed in the back, but he has a hard time listening when he's just freaking out. At this point I feel like our best option is to buy a safety harness for him to wear in the front seat, but I would love a way that he can feel more comfortable in the back.
<bot>: How do I keep my boy safe in the car? Should a buy a harness or should we continue working on riding in the back?