I just hope things don't go horribly wrong
and either dog or sheep don't get hurt.
Not saying it won't work, because in Mary's case it obviously has, but in my opinion it could be risky.
It's true dogs learn from experiences such as this, in fact I introduce feisty pups to Douglas in the same vein who tells them off but I know how he will react and can predict his behaviour. I am also covered with public liability insurance. Don't forget because it works for one dog it doesn't mean to say others will have the same success.
Alfie chased sheep when i got him but I taught him to be steady round sheep by doing lots of obedience work around them, he also has a rock solid stop whistle.
A combination of these two things were enough for us without ever putting my dog or livestock at risk.
Who pays for the vet's bills if it ends in tears?
Best of luck Sue, but be careful.