There is little more to say here than that Lefty is right. ROE should be law within, and only within a guild and proof needs to exist for violations to be dealt with fairly. No Guild Master should have to use up his supply of Enlightened Vision in order to settle disputes between members of his guild and any other player. There should simply be a record of hostilities that goes back a couple of days so that proof can be reviewed and acted upon.
It need not be very informative. Just who, whom and when. The where and outcome are irrelevant.