I have this problem also because I have to call Him by His real name when we are out in public, around His co workers or His children. In private I have to call Him Sir. For me the easiest way is to just say Sir after every sentence. It takes time and practice and trust me just yesterday He punished me because I forgot to say it. Punishment of this offense increases by 5 every time. We have talked about this and He is okay up to a certain point but He understands to a certain degree.