As with other materials such as wood or even stone, any spills of grease, oil, wine etc. should be removed immediately or permanent staining may occur.

To provide additional resistance against staining you could apply a specialist product such as  Penofen's "Knotwood" or their more advanced "Pro-Tech Composite Shield" which is designed not only to protect against stains, but to provide extreme UV protection and resist mold, mildew and algae growth.