So the ability says you use the attack role of an attack of opportunity for your weapon. So, other than the fencer trait, how else can I get bonuses on attack roles for attacks of opportunity (and therefore parries(y's?))?
Flank buddy with Paired Opportunists? Maybe?
Answering property on the weapon for sure.
Anything that adds a bonus to hit, I guess.
Animal companion flank buddy with Outflank, Paired Opportunist,and Pack Flanking. While you have those feats and a Menacing Answering weapon gives a +14 to parry. May get some pushback from the GM on that, though.