We really don't use the word sensei much in the dojo. We just call the person teaching by their name although if we are being more formal we may refer to the teacher as sensei when addressing them. But generally they prefer we not use the title. LOL I think they are still getting used to it since the dojo is still fairly young. If we have a seminar of course we always refer to the instructor as sensei when on the mat. And to be honest I don't think I can even talk to Mary Heiny sensei off the mat without addressing her as sensei, when she is visiting us... just seems wrong somehow.
There are only two teachers in my dojo that I refer to, in my heart, as
My sensei. You really can't separate the two in terms of one is
my sensei and one is
a sensei....they complement one another so perfectly it is like two halves of a whole.