Very nice! Consider also the cover of JHS's "29 Steps" book.
I too am waging the same compositional-battle. With a Basset, however, I have to compete with their clownish, comical expression. Being such a heavy dog too, I'll have to relegate him far lower on the canvas then your pooch (or JHS's). He'll be the base of an near-isosceles triangle, his body and my wife's forming a near right-angle on the right. The diagonal from her face to his will be echoed in the position of the arm of the sofa they're sitting on, as well as some background elements.
I'm also going to see what an application (within reason) of the Golden Section you advocated does to the composition.
I'll likely post some progress shots in the coming days (unless it bombs, but I don't think it will).