If you're worried about a situation where you are in a car, then you should learn to drive like the professional bodyguards. There are executive protection courses and so on that teach you how to handle a car like a weapon and use it to damage theirs so they can't pursue, run them off the road, and to break contact by recognizing the situation and getting hell and gone before bad things happen.
The movie "Proof of Life" has a perfect example of where that kind of know-how would have come in very handy. Had the guy who got kidnapped recognized the situation, he could have driven himself out of harm's way before it was too late.
If you're talking about being on foot, I can't really help you. I don't trust stun guns, pepper spray, or tasers because of their propensity for having dead batteries or not discharging (or whatever) when needed. Maybe a blackjack or spring baton would be a better weapon. You want to strike and get away, not stick around for the knockout punch. If you're up against more than one perp, you're in trouble anyways, especially when they know what they're going to do and you're just happening upon them.
I've never faced that situation exactly. Looking mean and in charge certainly helps--my dad has "the look"--like he'll kill you if you start anything. I wish I could intimidate people just by looking at them in a certain way. You have to look like you can carry out the threat, ya know?