Of course I always should say it all depends on your niche. There are probably areas where broad match can get out of hand without tons of negative keywords.
However, in response to the original question.. You could use broad match and get a list of all towns in the US and use them as negative matches, or use exact match because phrase match will not stop them.
I figure in the beginning of a campaign you are likely to lose some money by bidding on broad match...but as you weed out the "bad" words by adding them as negatives month after month after month you eventually get what you want without wasting much money. Or, wasting much less money than you are making by bidding on broad match in the first place. And, like Eljefe said, your negative kw list could become HUGE.