Here we go!
Your back up guys should protect you from muggers. If not theyre not watching out for you enough. To pull off a good mug, see if you can discern which side of the bunker your target is shooting out of, get your back up guy to pepper the target bunker to keep the guy in and go for it. if you dont get him, the back guy should. You can run past, shoot him from the side hes not using, or go over the top. The top is much riskier. Also if you run past it is more obvious to the marshall if he spins on you.
Try to pull off another move as soon as possible after the mugging. Capitalise on the confusion and communiaction lag and see if you can do more damage while they are still talking to each other and working out what just happened. Remember that the cheekier you are, the better. They just wont expect to see it happen...
Best of luck with it, although if you try and bunker me i will light you up like a christmas tree... Fair warning!