All dogs like the wind in their face when taking a ride in the back of a truck. You might have seen some dogs standing on the edge leaning way out into the wind. This may be fun, but it is very dangerous for the dog. Any sudden stop or turn could send your pet onto the street and in the path of other car. The risk of getting run over and killed could be high if this were to happen.
The safest way to haul your animal in the back is to tie them in. But there is a safe way and a very dangerous way to do this. If you should tie your dog in with another slack on the rope or chain that he or she could jump over the side, this would not be safe at all. The dog must not be allowed enough slack to jump over the edge. The rope or leash should be tight enough so that only his head is allowed over the edge without the risk of being able to jump over.
Here is how I have my truck set up for this. My pickup has some hooks on the floor in each corner. On these hooks I wired a chain to each side so it lays across the bed tightly right at the front. Then, in the center of the chain, I attached a leach that is just long enough so that when it is attached to the dog's neck he is only allowed to reach his head over the edge. There is not enough slack to allow him to get his feet up on the edge of the truck at all. This part is very important.
When attached in this method, my dog is able to move back and forth to either side of the truck bed but cannot jump out anywhere. He loves it! He goes back and forth from side to side looking over and feeling the wind in his face while being completely safe in case of a sudden stop or sharp turn. There is no way he can be dumped over the edge.