Strangely enough this is not as rare as you might think Howard...
I was dragged up on a sheep (amongst other things) farm in North Cumbria, and getting the balance right with a sheepdog is not that easy...too gentle and you end up with our friend Ci, too aggressive and you've got bleeding sheep.
With sheepdogs (border collies in particular) you need what's called a 'good eye dog', i.e. it will stare down any aggressive move, particularly from a ram, without flinching or blinking...and OK if pushed will give a little 'nip' when necessary.
Now cattle dogs are another thing...different tactics are required