Prevent cheating...

Found a way to prevent about 60% of cheating. The way is when I suspect that my opponent is using chess engine I use right click to draw a circle or arrow, one or two times. After that my opponent starts to blunder. Is this a good and legal way to prevent cheating?

Unless it's a shared study, your arrows and circles are only visible to yourself...

Yes, you are right .. tested. But I don't know how in practice it's work.