First, think about "what happens in your company when people use the 'back channel' of communications" - that is, the unofficial channel where gossip and innuendo can thrive, advises Rich Moran, the author of Nuts, Bolts & Jolts: Fundamental Business and Life Lessons You Must Know (Rooftop, $14.95). Consider: "Do people generally believe [the chatter]? If what people are saying is untrue, how do you work around it?"
Ideally, your boss views the "back channel" with a skeptical eye and won't take your scheming co-worker too seriously. But it's better to be on the safe side and take some protective measures.
If your performance review isn't due for a while, consider asking your boss to expedite it. "In a meeting that is specifically about your job performance, you should be able to tell where you stand and whether your boss is listening to the back channel," Moran says.
If the backstabber is a subordinate, you can have review sessions with people on your team -- even if official evaluations aren't scheduled for any time soon. "You should sit down with each of these team members individually and address how you want communications to work," Moran says. "Don't utter the words 'Do not talk to my boss behind my back,' but be clear about the communications protocols."
You could also call a team meeting and, without singling anyone out, let it be known that you want to create a culture of trust in your group "and that you won't tolerate behavior that is less than worthy of that standard," Moran suggests.
Whatever you do, don't ignore the situation and hope it will go away. More than just your reputation is at stake, since a team whose members can't trust each other is well on its way to total dysfunction - and that's not good for anybody.