I think male dogs are generally more aggressive and this is their way of saying, "This is mine, and this, and this..." I'm no expert, though. My Lefty uses his precious "reserve" of urine very carefully on walks--if he can smell that another dog has urinated on a particular patch of grass, that patch gets a steady stream from him as well. Other times he barely lifts his leg and just lets a few drops go--we call those "drive-bys."