The only way to stop them is to cut them out of the equation of your life. It can make the narcissist angry. That evil narc is beneath the level of contempt. Void of understanding and empathy. They just don't care who they step on and hurt in the process.
I was told once that two good people will never hurt each other. Ok actually i was the one scared of a relationship that's when I was told this. Then it happened, I started loving him more and more as time went by and still do.