Do I need to rebut every single thing the other side says?
No. British Parliamentary debating requires only that you engage with the important issues. You are absolutely allowed to pick your battles, and are allowed to make tactical concessions
(i.e. ‘We agree that the proposition's mechanism will work, but we say it remains unjust'). The point of rebuttal is to give sufficient grounds for rejecting the case of the other side, not hit every single tiny point.
Do I have to ‘flag up’ my rebuttal (i.e. indicate that what I am saying is a specific response to something said earlier)?
No, but you probably should. Your judges are, of course, incredibly intelligent, and if they spot the rebuttal they will credit you for it even if not explicitly flagged up, but even the best of us occasionally miss things.
Does rebuttal have to be at the beginning/end of my speech?
No. Put it wherever you like. If you do decide to ‘weave’ rebuttal, however, ‘flagging’ it becomes more important.
Final important thought about this stuff:
The distinction between rebuttal and substantive matter is false. It is a useful fiction for when you start debating, but can get in the way if an overly formalistic approach to it is taken. New substantive arguments can and often do clash with and defeat prior arguments, and what is labeled rebuttal often involves the making of distinctive new arguments and the bringing to the table of new information. All the rules require is that you adequately respond to, and defeat, the case of the opposite bench.
This guide is from the briefing published by the adjudication team of Koc Worlds 2010. The adjudication team is Can Okar (CA) Josh Bone (DCA), Julia Bowes (DCA), Suthen Tate Thomas (DCA), Will Jones (DCA), Handan Orel (ACA), Ozan Mert Ondes (ACA). This document is based on one drafted by Anat Gelber, Daniel Schut and Will Jones in 2007 for the Amsterdam Open.