A lot of dogs after going to the bathroom will kick their back paws. Why do they do that?

Dogs are territorial animals that will do all they can to let other dogs know where they were. All dogs have glands in their paws that secrete pheromones that are unique to each individual dog. The pheromones are activated when the dog kick their paws back. Its another way a dog marks its territory besides their feces and urine.

If you watch your dog in your backyard he probably doesnt kick his back paws. But if you take him on a walk where other dogs pass through he will kick his paws back to mark his territory.