Well, we'll have to agree to disagree on that one Dixie. Unless there is a sign asking me to keep my dogs on a lead I will continue to keep them loose but under close control - unless the situation warrants leads. I know that I am not being disrepectful, quite the opposite being a country gal through and through. I do however admire your ethics and will even supply the sharpened sticks should my methods get me in hot water.
I believe a dog can be taught not to chase (although I don't claim all ought to be), you just have to find someone who knows how to do it, has the time to do it and the determination to see it through. And thats the problem, who has the time, the knowledge and a spare place in front of the fire ?
I've offered to have the terrier here and put it through serious boot camp. I am confident it will learn that chasing is unwanted behaviour regardless of it being instinctive (not saying it should ever be let off a lead around sheep - but it should be on a loose lead walking to the side of its handler and behaving respectably, not pulling on a lead whenever something darts out of a hedge). But really there is no point because the owners husband will never be assertive enough to be the boss.
Problem is, its the relationship with the person who walks it that is every bit as important as the training - if not more important. You can't train a dog to have self control, and not to do something it instinctivly wants to do - and then just hand it over as 'cured'. Its a teamwork thing, the dog has to have total respect and confidence in the handler. I havn't done any research into this SHAK thing (sorry!) but I'd say that is the reason they don't re-home. Re-training the dog is one thing - training the human to grasp the concept and be the big cheese not just the hand that feeds is quite another.
It's quite simple, as has already been posted - if you can't keep your dog under close control at best or at worst recall your dog first time, keep it on a lead at all times.
This particular attack was 100% human error. The owners husband wandered off home without the dog when it dived after a rabbit, assuming it would come back. He's my friend, but he's a bloody idiot - who won't do it again. The dog found its own way into a sheep field and had no one to tell him it wasn't ok to go get the galloping woolly things. None of us would think about wandering off home without the dog would we?!! Still feel sick for those poor wretched lambs. All the sheep in that field are still traumatised and bolt as soon as a dog is walked along the footpath. Horrors.