I'm kind of thinking something like roll cage tubing spaced 3" apart and welded to the roll cage and bolted to the floor should just about do it. I think my dogs could get in the front seat of a paddy wagon with all paws handcuffed behind their backs. My puppy ate 3 of my seatbelts in half and tore the door panels up on my Cherokee. Because another car parked next to us with a dog in it. Thankfully, that’s just a beater vehicle. Makes me wish I’d have gone for one of those calm submissive obedient breeds like a golden retriever or something.

 

Like a poodle.........

 

I toss my dog in the back of my unlimited, and have no problem keeping her back there. But it's not training. She's a 90 pound Great Pyrenees, and she literally can't squeeze between the top of the seats and the roof.

But she does have lots of room back there. Keeps us both happy. (I used to drive around with her in the cab of my 69 Ford 3/4 ton. She took up 2/3rds of the front bench. Sometimes that 2/3rds included my lap.)