If you have any doubt about your employees’ willingness to adhere to the organization’s IM policy, content guidelines, and usage rules, consider applying a software solution to your people problem. 
If you opt for an enterprise IM system, be sure it comes complete with content monitoring and filtering capabilities. If you allow employees to download personal IM software from the Web, install technology that works in concert with your IM policy to detect and block messages that incorporate banned language or otherwise violate your content rules and usage policy.
IM Rule # 21: Instant messaging rules and policies should guide technology, not be guided by it.
Nancy Flynn, The ePolicy Handbook, New York, AMACOM, 2001.