Why not build this in World 6? The whole prospect of Gondor is that you will have defenders. No one will be strong enough to 'defend' once W7 hits, we'll all be newbs together. Maybe make a 'challenge' system where you can spar for the right to be a defender by challenging one of the current defenders... this way we always have the best defenders.
As lawspeaker you would approve of each defender or reject them for moral failings, so we always have the most noble defenders. Better yet, you might want to check them out and approve them BEFORE they are allowed to challenge.
Also, this would encourage a strong standing militia as many would like to eventually become a defender. Once we hit 6 rings, maybe the 1st ring gets cleared out and becomes a ring of nobility... where strong fighters who wish to be active in empire defense would be allowed a 'defender-like' commission since they will have strong abilities but by that point few could challenge the deific power of established defenders.