My lover/Master and I are both in the SCA-medieval recreation-so My Lord fits for us; I don't know how awkward that would be for you. I also often call him Beloved, because he is that, whether we are having a vanilla night, he is topping, or we are playing switch for a bit. As 'Dog' is part of one of his nicknames, he actually had me use his legal first name for a while--he wanted to be sure that we both knew who I was playing with. (In Carrie's Story by Molly Weatherfield, the Domme always has Carrie use his first name, so there is some precedent, if only fictional.)