I saw a few posts kicking around about co-working and sharing space, so I thought I'd mention that access control systems are definitely the way to go.  Handing out keys that say "do not duplicate" is SO last millenium.  An access control system allows you to give somebody a card, disable its function in an instant if necessary, and even record comings and goings.  Very nice, and can give you peace of mind.  Some of the higher end stuff  gets expensive, but can include fingerprint and facial recognition.