I will be the third to heartily recommend Mr. Dobson's book. It is an excellent resource and is quite thought-provoking if you let it.
I think O'Sensei's angle on verbal self-defense was simply 'shodo o seisu', controlling the first move. You can use your voice, among other things, to attempt to control a situation before/as it happens ("kiai" is a great example).
Anything that reinforces establishing control would likely be a good complement to your aikido training. I tend to enjoy this piece of the puzzle myself, since talking is so damn easy.