How do you figure that? It just means "teacher", it's how Japanese schoolteachers are called. You surely don't think every elementary school can only have one sensei? This is getting a little too "Highlander" for me.
I am only speaking as far as commmon sense here goes - the senior instructor, or the owner of the dojo, is customary called Sensei here. Actually it must not figured out - once you attend the dojo it easily spotted the person wh is to be the 'Sensei' in this "common sense" setting.
As for settings that are no longer common sense, I already said who is the Sensei then, for me :-)