Our little Jack Russell, Zip is all about squirrels, deer and rabbits. She does know the word no and when said firmly it locks her up. I did need to use a shock collar, but she's so sensitive usually just the vibration signal is enough. I did have to use a bit of juice a couple times when she didn't respond to command or vibrate. Im don't like using this, but its important that i can stop her if she's headed toward danger. Jack Russell s are very good at reading emotions and usually just tone of voice is enough.