I had an interesting exchange with a colleague yesterday about a proposed technological solution to a problem that's not really technological at all.
A business, if I read the proposal correctly, wanted to give other businesses the chance to lock out employees from systems after they've left the company, especially if they were fired or laid off. There are actually a lot of ways to do this, and anyone who has a half-way decent security system should be able to lock people out once they've been let go. (It's nearly impossible to fully protect data someone has access to while they're working. If they really want, they can always take notes by hand, do screen captures, or use a bunch of other means.)
The issue in this case, though, is more an issue of how to manage a layoff or firing than how to lock someone out of a system. It's more important, for example, to do things in the right sequence: take former employees away from the system (for example into another room or out of the building), ask for their ID card, turn off their access, and not let them back in, as well as give them their final pay or severance only after they promise in writing to bring no harm, do no theft, and so on. Here are some HR-style tips from Entrepreneur.com on how to manage the process to avoid a lot of legal issues. On the technology front, I'd say it comes down to thinking through the security issues and holding to them in a mannered but firm way.
I've helped businesses large and small through just such issues, and the solutions have always been logistical and managerial, not technological.