Teach your dog to keep well away from the sheep when flanking.
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If your dog's going to work sheep or cattle properly, it must learn to give them plenty of room. Of course there are times when the dog needs to be close and assertive with the stock, but as a general rule, the less the dog pressurises sheep or other livestock the better.
If the dog keeps well back off the animals, they'll be much calmer, and subsequently far easier to manage than excited or frightened animals will be.
In this tutorial, you'll learn ways of encouraging your dog to go out wider, and keep well back from livestock.