Under shared folders, we have a shared calendar for a lab at a school. Teachers are able to add appointments and edit or delete their own but not other user appointments. This would work fine normally, but some teachers are ignoring the fact that there is already an appointment scheduled in that lab. They put their own appointment at the same time so it now has the lab checked out to multiple people at the same time. Is there a way to stop people from putting in appointments if there is already something scheduled at that time? Thanks for your help in advance.