The best suggestion that I could give would be to assign each space a number and then have people log into a system to reserve the space. At Deloitte they have this type of system and it seems to run smoothly. People actually check into a space every morning and check out every evening. And they also can reserve the space for weeks at a time if they would like. The system runs like a kiosk system similar to reserving airplane seats. I believe it was an internal system they had, but there are probably more systems out there like that. Or you could simply create a position in your office where people would check in and check out with one person to handle this type of system. A simple database could track it daily if necessary also.