Are there any natural ways to stop teeth clenching/grinding?

Nothing: Nightime teeth clenching/grinding is called nocturnal parafunctional bruxism and is considered one of many sleep disturbances called parasomnias. Everyone does this at night during normal partial arousals from sleep or during transitions between wakefulness and sleep. The best way to manage the negative effects of bruxism is with a nightime devise or nightguard.

Maybe.: Some people, but not many, have been successful using relaxation techniques such as meditation, bio-feedback or yoga. Physical therapy with behavior modification is also available.

A few ideas: Read this: Bruxism Maagement (http://emedicine.medscape.com/article/2066277-overview#aw2aab6b7) Recommending options include: appliance therapy, occlusal treatment, medications, relaxation and behavioral strategies, Sleep hygiene. See TMJ expert for expert advice.