I like the idea of this photo, the problem is that whilst the primary subject is well composed (if a little closely cropped to his hat); the secondary subject isn't. I find that my eye is falling on a the clump of grass in the upper left hand corner, instead of on the rhino which is hidden somewhat from view at a point where there isn't any composition to draw my eye toward it.
I know you can't just move closer (always) in these situations nor ask the rhino to move, but I feel that the rhino really needs to be where the clump of grass is to make it stand out well for the shot (at the moment if you didn't mention rhino in the title I bet some would miss it totally and others would think it just rocks.