Years ago (in Atlanta) I had my purse stolen so many times (usually the purse costs much more than any contents inside), I switched to cheap (I called them "disposable") purses - and started keeping cash/ cards in another location (pocket, shoe, bra). Straps that crisscross the body and making a LOT of noise also helps...
Lastly, I agree with 2miles - a big Machete is a handy tool as well (rob me at your own risk)