If you have a behavior modification plan be sure to document the plan and monitor progress. Be wary of hiring employees with a history of harassment. If they did it before they can do it again. Do not assume complainers are out to cause big trouble and file a lawsuit. My experience is that most complainers just want the problem taken care of so they can get on with their work.
Perception is reality.
Even if the actual harassment is not taking place the perception that it is can cause problems. Harassment is one of those really tough business issues because it is a social issue that has not been resolved. We do not even have a good working definition. Harassment can run the spectrum from stalking to inappropriate looks and even into areas that have not been 'invented' yet. Harassment can be found anywhere you find different human beings which simply translates into anywhere.