You will never be able to prevent someone from suing you, especially if they get seriously hurt or killed, be it by martial arts or a firearm. The best defense is making sound and reasonable judgments regarding your use of force. I would personally prefer to have the option of using martial arts techniques to handle a situation that MIGHT have been a "shoot" scenario without additional training and experience. Are you going to supplement your Muay Tai with some form of grappling? I have found that I use more throws/grappling than strikes for LE work. It seems, for me, that bad guys don't want to stand a fight, but resist once you put your hands on them. Dunno about your department, but Taser and sprays are lower on the force continuum than strikes, so depending on how your admin is, they may prefer you start with them, situation dependant, of course. Just a thought.