Tips on focusing fast moving subject?

Thats a tough shot.  I would consider going to a higher Fstop to increase the DOF, and increase the ISO to compensate.  It will make the camera a little more forgiving on focus errors.  You will also find you will under expose due to the snow, so I would compensate for that as well.  Centre focus on the dog should help.  Burst mode may also help you get a good capture.

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Glenn