Dog verses cat

Question
I need help with helping my adopted mini aussie to accept my cats.  When Sam first came to our house he was on good behavior and seemed to ignore the cats, however, now that he is part of the family he seems to be out to get them withthe exception of our very old cat. The old cat has been able to stay upstairs because Sam accepts her perhaps because she mainly sleeps.  He has rushed her a few times but this old gal has been there and done that so she ignores him.  My younger cats are full of play and grew up with aussies. They did not have any issues with Sam at all until he decided to rule them. I do not think this is a prey problem but more of a control herding problem. It has become so bad that I am keeping the young cats in the basement for peace and perhaps their safety should Sam take it too far. Sam seems particularly to go after darker cats so perhaps something in his background before he arrived here.  Would clicker training help some way here or what do you suggest?  I also have a 4 year old aussie and a 6 month old aussie that do beautifully with the cats -even play with them.  

Answer
I'm curious if you got your other dogs as puppies, or if they already had experience with cats.  If this dog is an adolescent or adult (over 4 months of age), it's harder to alter this behavior that it would have been in puppy hood.  The fact that your other Aussies get along with cats is irrelevant to this dog, who may have stronger herding instinct or prey drive.  Clicker training certainly can help your dog be more under control, though, so, yes, go ahead and start that if you are knowledgeable in the method.  After all, shepherds can stop their herding dogs in place even when livestock is present.  However, I would not expect this training to be foolproof when you are not present to direct the dog, as predatory instincts are very hard to override, if that is indeed the issue.  In any case, there's a terrific book you may want to get - it's called "Chase! Managing Your Dog's Predatory Instincts" by Clarissa von Reinhardt. I think you may find some helpful hints there.  Meantime, you are doing the right thing by having a safe area for the cats.  Aussies are one breed that is often problematic with cats, and some will only accept the cats they knew as puppies and reject any new cats they encounter.  Others will not chase the household cats in the house, but if they encounter the same cat outdoors will chase it.