Shortening the rope

'Enough rope to hang one's self' isn't really an analogy, but more so a figure of speech. The 'and then a couple of more feet, just to be sure' was really just a joke meant to point out how Unix gives the user many ways to hang one's self. 'Shortening the rope', on the other hand, is a play on that to mean reducing the amount of ways one can hang one's self.