From Jack's Mom (remember, they live on 60 acres of doggy distractions):
I let Jack out with his long line attached, but I did not pick up the end and we headed down to where the agility area used to be. He was his usual silly self, running around chasing my feet. I looked back at the kennel because the Jack Russell was raising a ruckus about something. No more than a few seconds went by before I looked back around for Jack and he was high-tailing across the field towards the old burn pile. Now, as you know, you do not go running after a Border Collie. For one thing humans don't run that fast and the other thing is you have now started the "Chase Game." No winning that one. I looked down at my wrist, at the whistle hanging from it and thought "here goes nothing." I blew a short blast. Jack heard it, spun around and came back, flying low across the field. He was greeted with lots of whoops and cheering plus plenty of cheese.
So I can say it works!! Thanks so much for teaching us this great cue!!