I've been in that situation twice so far, I'd think something like save up a minimum of say 6ap for an 11% defense increase up to perhaps 9 for a maximum of 33% damage reduction from physical sources, perhaps a talent could have something added in to add magic damage reduction along with whatever current bonus it has, or perhaps just one more fresh one to pick from if you find that play style suits you. Or perhaps a flee talent/skill allowing people to run away without attacks of opportunity, then imposing a penalty on them when they are x spaces away from any enemies, x being estimated safe distance or proximity to an ally altered by the amount of moves they had to make to get there, the penalties could be varied or stacking for a bit, you get the idea.
