You did not say if youre shooting ditial or film. I set my exposure the same way in any event.

If I were going to shoot that, I set my white balance, and then I'd set my exposure for the white on the dog and then just let everything fall into place. Spot meter the white on the dog and open up about a stop and a half or meter the black and stop down the same. If the light will change a lot, it will be more of a challange - shoot raw and you can later change the white balance if needed. As per exposure, use the histogram to make sure you not clipping the white, unless you have too. . .

You might also use the sunny f16 rule too. . . Simply put, the rule tells us on a bright sunny day to set your aperture at f 16 and convert the ASA or ISO settings to the closest shutter speed.

You might also try metering the sand, it might be middle gray as are most green planst. . .