Getting rid of a live-in maintenance guy... questions.

[Chris Ball]

Anyone have advice for the best way to get rid of a live-in maintenance guy who has the keys to pretty much everything? He doesn't have the master, but he has individual keys to the gates and all the units. We recently bought a 20 unit complex and he was part of the deal. Unfortunately he hasn't been working out for us and it's time for a change. We'd rather not change 20+ locks, but we're not confident we'll get all his keys. How have others dealt with this? Thanks, -Chris