Update - I found Unlock Grades or Items in the Faculty Role - Course permission settings. I tried setting this to Prevent - thinking that this would remove the Faculty's ability to lock or unlock the gradebook. But after saving the revised Faculty Role settings - entering the course as Faculty - I could still lock or unlock the gradebook. We wish for the locking of the grades to reside with the Dept. Head or Chair.
Again, I thank you for any help you can provide.