On Wed, 17 Sep 2014 15:11:25 +0100, "Nightjar \"cpb\"@" "insert my
surname here wrote:

Night vision goggles will allow you to do that and, I am very reliably
informed, are also good for spotting poachers. Of course, you may need a
pair for the dog as well, if it has to see the sheep.

Paint the dog in luminous paint.
Or do this...
https://www.youtube.com/watch?v=EbqWhSA3BVU#t=55