Add a new attribute – something like “Enforce Uniqueness” – to the Common Fields setup window. It can be grouped under the Options heading just underneath the Required Field attribute. Users can tick mark the box or leave it unchecked. Then add some type of downstream verification check, ideally at the Dropdown List Level: When the user clicks into a field’s drop down list, check to see if Enforce Uniqueness is selected on that field. If Yes, compare the user’s selection from that list to the existing values for that field in the database. If there is a match (i.e., saving the selected value would result in a duplicate) then reject the entry and give the user a message like “The selected <name of field> already exists. Duplicates are not allowed.” Alternatively, it would be ok to check for duplicates when saving the contact data. WA is already doing field validation for Required Field during saving, so just extend that check for user fields deemed unique. It would be ideal to reject duplicates as early in the workflow as possible but checking during saving would also work.
ps. The creation of duplicate contacts is the biggest challenge we have with the system. We're a HOA, and since only the primary email is unique in WA, spouses and other family members are creating duplicate contacts with their own email addresses.