To really do it right, you need to implement user level security (not an easy
task). You make sure that the users can't get directly to the tables. Then
create a form that does not allow editing or deleting of records. Data entry
would be OK. If they need to modify other data in the form, you could turn
Enable = False for that particular field if there is data in it. This would
require code in the form.
If you don't want to go through all that trouble, you could just do the
coding on the form knowing that there is a risk of a user going directly to
the table or messing with the form.