When I lived down in Texas I went to a herding training event with my boss one time. She had Aussies (at the time I had one of her dogs, too). Her boy went and herded sheep around the ring - did a wonderful job - then came back and peed on her. I don't think she ever figured out why and I think it was the only time he had ever done that.
Who knows what goes through the mind of a male dog when they do things like that.