How do you stop a narcissist from attacking in a business relationship?

Read first and foremost. Gather evidence, and report them to your HR dept when the time is right. Be warned that they are extremely paranoid and are character assassins so keep your paperwork, thoughts and feelings to yourself. Do not gossip about them, Do not gossip about anyone else either as they will use that against the person AND you to isolate. They will use personal info to destroy your confidence and credibilty. They WILL lie and cheat, they DO NOT play fair. They believe that there is a conspiracy and a plot against them ( and its hardly suprising to find that due to their behaviour people are!) If they sense this, they will start to gather evidence of YOUR trying to destroy THEM! and will start up a hate campaign against you to isolate and destroy you. But do not second guess yourself. They are predators and I believe they are a milder form of psychopaths so be very careful. If you want to empower yourself try ignoring them as it works better than any words and they cannot stand it. If things get to you and affecting your mental health , consider moving on, its just a job.