Prevent user from duplicating value

Idea created by Salemation on Dec 18, 2013
         Dears Esri supporters,
         I would like to know the solution to prevent a user from duplicating a unique number into a specific field.
         Let's say the first house is 1 .. I want to prevent the user from entering the same number "1" into the second house and prevent the duplicate?
         So upon editing the attributes of a specific map, it prevents the incident of duplication. Like giving him an error dialog or a hint that he is duplicating a specific number.

         or if there's a solution at the end of day a list of all duplicates shows up and the administer has the permission to Cancel only the recent duplicates.
         Thanks in advance