would be pretty simple via a macro:

Basically,
Have the macro author the formula ChemistB put up into two columns - then lock the values.

Then, have the macro 'flag' any cells with a count greater than 1 (may be tricky to make fast, think I could do it though) - Rekey -those cells (add the formula again) and then lock values... check for uniqueness again (if the SUM of the counts columns = the COUNT of records, you are good to go...)

That way it would be automatic and unique :D