Best way to "repair" a missing required field

Best way to "repair" a missing required field

I have a date field which is now required.

I have a few hundred records which were created before the field was set to required.

Most of my users prefer to do in-line field edits rather than going into Edit mode.

If the user is not editing the required date field, then the built-in "required" functionality does not trigger.

How do I force/notify the user that the field must be entered?  I think that a client-script might be the answer, but

I'd like to force the user to enter it when they do any other in-line edit in the Deal.

I'm unsure how to approach it.

Any guidance and insight appreciated.