how to prevent a value from ever changing

problem: within the DB there is a special "empty" string, this string
must never be changed.

how to best enforce this rule?

Currently I have....

problem: within the DB there is a special "empty" string, this string
must never be changed.

how to best enforce this rule?

http://agilewebdevelopment.com/plugins/attrlocked

Or something similar to that maybe...

Currently I have....

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# override the string_value setter,
# to control empty string from ever being overwritten
# ensure that the single empty string is never modified
def string_value=(sv)
   if self[:string_value].blank? && !self.new_record?
     raise "Empty String May Not Be Modified"

       #errors.add(:string_value, "Empty String May Not Be Modified")