Shielded Caster

Whenever you are adjacent to an ally who also has this feat, you receive a +4 competence bonus on concentration checks. If your ally is wielding a buckler or a light shield, this bonus increases by +1. If your ally is wielding a heavy shield or a tower shield, this bonus increases by +2. Finally, if an enemy threatening you and your ally has the Disruptive feat, or another ability that increases the DC of concentration checks, the amount of the increase is halved.