Two hunting seasons ago my dog Gauge thought it would be a good idea to jump out of the back of my truck. Man, was that scarey. He had been in the back of my truck many times before and never had a problem. If going more than a mile or so, I would put him in his kennel, but we were going just down the road, so I let him hang out in the back of the truck. Sure enough, when I got up to about 40 MPH, I looked in my mirror and could see him launching himself over the side. Did I mention my truck has a 4 inch lift, so its a ways up there. He hit the middle of the road and started tumbling. I hit the brakes jumped out of the truck and expected to see broken legs, if not a broken neck. He sort of sat up and I could tell he was thinking, "what the heck just happened." I looked him over and could only find a few cuts on his face and and mouth full of dirt. His eyes had a lot of gravel in them as well. I took him to the vet to be sure he didn't have a concussion or any other injury I couldn't see. Other than the cuts, he had a clean bill of health. The vet even said he could hunt the rest of the day if he was willing.
So we returned to doing what we came to do, hunt pheasants. I let him out of the truck in the next field we went to and he was ready to rock and roll.
I couldn't believe how lucky I was that he didn't get injured more than he did. I think his saving grace may have been his youth. He wasn't quite 2 years old at that point, and all I can think is he was a lot more durable than an older dog would have been.