Single use macro in command button

Hi guys

Below is the code assigned to a button for inputing the time when we book a driver out, what I am looking for is a way for the button to only be used once... so if a driver books out at 08:00 then the time wont change if the button is pressed at another time

Sub Bookout()

    ActiveSheet.Unprotect
    ActiveCell.FormulaR1C1 = "=NOW()"
    Range("F3").Select
    Selection.NumberFormat = "h:mm"
    ActiveSheet.Protect DrawingObjects:=False, Contents:=True, Scenarios:= _
        False
End Sub

Thanks for your help