My Greyhound Hates Small Animals?

I have the sweetest and most gentle greyhound ever. But when he sees a small dog or any small animal he goes NUTS and turns into a ferocious and vicious dog. He even bit me one time because I was trying to pull him away from this other small dog. Does anyone know the best way to train him without taking him to a dog trainer? It’s to the point where I can’t even take him to get him groomed because he grabbed a cat once while they were taking him back to get washed. Thank God the cat’s ok. It clawed his face pretty good though. Any suggestions?