Tony, Sars and CO have almost identical constitution. I tried the invisible fence with 3 CO and it failed. I did all the right things, watched the video, trained them etc.. took about 3 weeks.. and then one day they just walked through it and sat down in the middle of the hot and tried to scratch the collar off. If alerted or defending - the invisible fence will not contain a Sar or CO. I have one I can send you if you want to try it... don't buy it. Let me know. Gary