I'm not sure what Rocky is up to when he does this.
He starts out by sniffing a certain area.
Then he starts desperately digging with his nose.
Then as if on some radical drug, starts rolling around in the area he sniffed.
I had a dog once that would do the same thing. I think what he's doing is trying to disguise his scent. He finds something stinky and rolls around in it to mask his own odor.