There is a good book out by George J. Thompson called Verbal Judo: The Gentle Art of Persuasion. It is written by a former policeman and black belt in Judo. It describes a lot of what you talk about.
I used to be a Security Guard and it helped me tremendously in dealing with difficult people. It is very big on not meeting your opponents force with force (i.e. threats with more threats) and is therefore very aikido-esque.
Scott in Kansas