How Can We Create a No-Social-Media Policy for Our Office Handbook?

Everyone, as a company, we would like to introduce a policy on the use of social networking sites. We would like to add it to our staff handbook to inform employees that they are not supposed to access social networking websites in the office.

Please help me with content for such a policy. I did a search on the internet, but most of them are talking about limited use of such sites, whereas we don't want our employees to visit/access such sites.

Looking forward to your help...

Regards,
Gaurav