My Dog is attacking/going after other animals that cry or yelp. Why?

Corgis have prey drive that is through the roof. Any kind of distress call from another animal can trigger them into action. There have even been accidents at dog shows in which smaller dogs have been lunged at and killed as prey. This is an asset when working in close quarters with large cattle, but not when they are in a pet environment around smaller animals. Given that the dog has this degree of prey drive don't leave him alone with smaller animals. He can be trained to keep it turned off when you are present, but you can't control what he does when you are not right there. A trainer experienced in working with high drive dogs such as police K9s would be very useful here. Their dogs have to be under complete control even with squirrels and other prey animals all around them.