Can my dog ride in the back of my pickup truck?

There's another aspect of letting dogs ride in the pickup beds:

Last winter, my son had used his large pickup to pull out his stuck tractor, threw the snatch strap onto the lowered tailgate and was backing it up the driveway, having noted that the 2 family dogs were far away from him. It seems that elderly Banks, the Catahoula who ALWAYS rode in the truck bed, didn't want to miss a ride, so must have raced up to the truck and then missed the jump. My son ran over and killed his beloved dog.....