While you should train your dog to not chase strangers by obeying your commands, (I use the single word, "Halt" with my dogs) are you sure you really want to train him or her not to bark at strangers?
After all, that's what dogs do best as they alert their pack and alpha leaders to potential threats- and you should take the reigns as alpha, i.e.; Leader of the Pack, if you are not doing so yet and let the canine(s) feel good about helping you.
May I respectfully suggest that you focus on letting the dog bark until you've had a chance to determine if the stranger is friend or foe and then introduce another command, "it's OK," after you determine such?
I also make a point of shaking the hand of a stranger to my dogs - even if I know the human - just to let the dogs know I'm not feeling threatened. Reduces my slobbering, English Mastiffs to mush, everytime, so I'm guessing it works reasonably well with smaller breed dogs, too! :)
Sign up for an Obedience Class at a local AKC (American Kennel Club) Chapter. Most don't care if your dog is a pure breed or a mutt, but the good ones with their dog loving volunteers will help you develop your dog training skills and they often add unimagined hints for dealing with other doggie behaviors. The costs of the classes (an hour or so, once a week, for eight weeks) are usually minimal as most only cover the cost of training aids and photo copying.
You and your dog will be happier for the experience. Good Luck!
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