The second course of action, which I employed recently when I discovered some particularly rat-faced specimens sniffing around the back of my house, is to shout obscenity-laden abuse whilst brandishing a metal chair leg. If you take the second course of action you must give the impression that you are mentally unstable, care not for your personal safety and that you are capable of unprovoked acts of extreme and random violence. You have to unleash without reticence: the more spittle, the more violent the threats and the more unhinged the profanity, the better. Just conjure the vilest words in your vocabulary and string them together like a jazz-poet with Tourettes. If for a minute they realise you are bluffing and that you are in fact a physical coward with no martial ability, you are done for. Despite being genetic flotsam and jetsam, junior scum-bags have acute fear detectors.
The American version, of course, simply replaces “metal chair leg” with “12-gauge shotgun,” but I believe the general principle is still there.