Not Allowing Entries to be blank

I have a cell that is formatted for a date that will get updated by the user (F4 Below).  And then column A is just copying that value all the way down.

I want to prevent the information in column A from being deleted accidentally.  It will likely be a hidden column, so accidentally deleting it is possible.  I tried data validation and rules, and they worked in all cases except if they are deleted.

How can I prevent A1 from being deleted, but still have the user be able to update the date in F4 and have A1 update.