Dog tries to kill cats

Question
Hello, thank you for your time,

I am very concerned. I have just recently adopted a German Shepherd mix from the local SPCA. His name is Jack, he is fixed and is four years old. He is a perfect dog. He gets along great with our previous dog, a beagle named Scout.

He is already protective of our house, which is good. His bark is extra security and it's comforting having him around the house. Unfortunately, one of his instincts has become an enormous problem.

I heard my girlfriend screaming last night, ran out of my room to find that Jack had caught a neighbor's cat in our back yard and had it by the neck, jerking it back and forth as if to kill the cat. It was a rough instinctual side of Jack we hadn't seen before, and it was a bit scary. I was able to separate him from the cat with a loud yell of NO, and LIE DOWN. But I fear his cat killing days can cause great trouble in our neighborhood. The way our neighborhood is setup, our house shares fences with FIVE different properties. I see a ton of neighborhood cats and would hate to see Jack kill one of these cats. He is very quick and charges at them like a lion. I don't doubt that he can't catch more.

It worries me greatly that he will kill one in our yard, or worse, get out of the backyard and kill a cat.

What can I do? I really don't want to take Jack back to the pond, but wonder if this is inviting trouble. What would the pound do with him? The SPCA had the note that Jack was actually good with cats.

He has quickly become part of our family and I hope there is a way to train dogs away from this? Just tonight, a cat was in our backyard and I literally had to grab his collar to keep him from chasing it.

Please, I hope you can provide me with some guidance,

Jimmy


Answer
Experts here have a number of buttons to click on for each question.  Perhaps I should have clicked on ''This is our of my area or I just can't help,''  I do not understand why cats are allowed to run loose, but dogs must be fenced in.  You could take the stand that cats are safer out of your yard.  He may have accepted a certain cat in the house as part of his pack and to be accepted and protected.  Strange cats living in another house are another matter.

I feel justified being listed her as a dog expert because I have a wealth of experience starting with a well bred puppy and making a fine dog out of it.  Nobody has all the answers.  Some problems may not have a good solution.  I don't even know where else to send you.