I have a 2 year old Australian Cattle dog. Had him since he was 8 weeks old. He gets very excitied when I put him in the truck for a ride to a field where I let him run free and play. When approaching the truck he gets excited. After loading up he starts excessive barking and jumping back to front. Also nips (grabs, not hard) my hand as I get in like he's telling me hurry up and get in the truck. I have engaged the center rear seat belt and attsached him so he cannot jump to the front. I have tried leaving him in the back seat, closing the door and walking away. He quits barking. When I return to the truck he starts his none stop barking again. Any suggestions?