The real reason to why dogs do this is to mark their territory. Canines have scent glands in the back of their feet, and when they kick against the ground they are trying to leave behind their scent. Dogs who are dominant will do this with the goal to warn others dogs to stay away unless they want trouble.

Why do dogs kick their back legs?

“Dogs shake or kick their legs when you scratch them because of something known as the scratch reflex. ... It activates nerves under his skin that are connected to his spinal cord and relays a message to his leg muscles to kick in an attempt to get rid of the irritant.

Why does my dog kick like a bull?

Dogs and wolves kick their back legs like a bull after pooping when living in the wild. ... This is also known as the way a dog marks his or her territory. Dominant dogs mark their territory to warn other dogs to stay away, while non-dominant dogs are simply leaving a note saying they were there.