Physically, ju-jitsu can be very effective against someone larger than you are, if necessary. Aside from being an excellent way to stay in shape, it might be something you could look into to gain an edge.

Other than that, I concur with _ID_, if you have the mental side locked down, you have your pet locked down. Which is really my favorite way to gain someone's submission, knowing exactly what makes them tick to have my way. Reading up on psychology can be very helpful in that regard, if you have an interest.