Sorry, I know this isn't quite a response to the original topic, but Devonlady: I'd like to hear more about your whippets! Is that typically whippet behaviour? I need a dog to free range with my chickens - unfortunately my friend's Jack Russell terrier doesn't quite qualify for the job!
I have whippets, pugs, a greyhound, an Ibizan, a border terrier and a yorkie and can't say whether it is breed trait in any of them. I can only think that the sheep, poultry and pigs are regarded as part of the pack. I have a feeling that if a strange dog were to be brought in it may upset the balance.
If I were to choose a dog for guarding poultry, I think I may go for a traditional guarding breed. Or a Border Collie could easily be taught to respect poultry.
Sorry, I'm not much help but maybe if you got a whippet pup it would be fine. You would need to be VERY firm though in the first instance.