How can I prevent changes to an event's attendance?

An Event can be locked to prevent future changes. To lock an Event, use the Verify Attendance button next to the event. This can be found on the All Events screen:

... or on the detail page for the event:

At the bottom of the attendance list, there is a checkbox labeled Finalize Attendance & Lock Record. 

When this checkbox is checked, Rescue Hub will prevent any future changes to the event, and remove any attendees that are not marked as Absent or Present. 

Once an Event has been locked, it cannot be changed unless an administrator unlocks the record. A locked record will look like this: