How do I prevent leaks of IP or secret information through leaving employees?

I have seen this problem happen several times throughout my career and have been involved in major litigation between companies and employees and former employees over this issue. Companies should institute procedures and policies on what happens when employees leave. There should be clear policies that instruct employees what they can and cannot do after they depart. There should be documents stating these policies that the employees sign on departure, so that there is a record of their knowing the policies. It may also be appropriate to notify their next employers of the restrictions on departing employees. All of these issues are very fact specific to each situation, and so consulting an attorney is advisable. Steve