Users at Lake Bank have been creating multiple events for once in a lifetime event...

To prevent users from accidentally creating more than one event of such an event type, the Admin should create a validation rule that will stop the user if they attempt to add multiple one-time events. A validation rule is a rule that verifies that the data a user enters in a record meets the standards you specify before the user can save the record. By creating a validation rule, the Admin can ensure that only one event of a certain type can be created for each contact.