Use a text field and give it an auto-entered calculation that combines the data from both fields.
Now you can specify a unique values setting on this auto-entered calc field.
Yes, it works that way. I would like additionally to:
a.- if a duplicate record exists go to that record and display a warning message. I guess I could trigger a script when I exit the 2nd field ... but how would I bring the duplicate record up ?
Use a self join relationship that matches on this field or the original pair of fields. Go To Related Records could be used to find the original record.
Here's a relationship that matches to all records with the same values in Field1 and Field2 without matching the current record to itself:
Table A::PrimaryKey ≠ Table A 2::PrimaryKey AND
Table A::Field1 = Table A 2::Field1 AND
Table A::Field2 = Table A 2::Field2
and now IsEmpty ( Table A 2::PrimaryKey ) will be true only if the combined values of Field1 and Field2 are unique.