Whirly I was taught that if you get this put your first knuckle of your first finger just below there sternum and rub it up the way not very hard. It is bloody sore and if they are still alive they will move to protect it. Strangely enough it was taught to me again as a pilot incapacition check during a sim session.
The biggest problem i had with a student on the controls wasn't huge bloke but a 85 year old granny. She kept on grabbing the controls with both hands with a solid grip and fighting opersite way every time i put a control input in. And no amount of talking to her would make her release.
In the end I peeled her fingers off the controls pitched up to 20degs and pulled the catch on the seat so she went back and couldn't reach the controls again. And thankfully we had landed by the time she had managed to shuffle the seat forward again. At which point she grabbed the controls again in the grip and didn't let go until I had shut down and got out the aircraft.
Well done though getting a sale though
MJ