Well, I can't say for a Sar or CO with invisible fencing, but I had a Chow on 2 Acres with the system. She went through the training and respected her border..... the majority of the time. As Xamen said, we were constantly splicing the wire due to rodent damage. The thing about Grizzly is that she was very smart and would constantly test the parameter. If it went out, she went exploring. Also, if she saw a threat (another dog or human) she had no problem bolting across the threshold to defend her property (once she was across, she wouldn't come back aross the hot zone either). She was only 50 lbs. and I had it on the highest setting. I can't even imagine what a dog with a Sar or CO's stature would do... 8O