[Aerich]

With the feat "Lingering Song" (makes a bard song last for two rounds after the bard stops singing), a bard can stack song effects, even those from the same song. War Chant (the lvl 11 bard song) regenerates 3 hp/round, grants +2 AC (generic), and gives 2 DR to slashing, piercing, bludgeoning, and missile damage. Hence, if you have the patience to pause the game and click the bard song icon numerous times, you can stack enough AC and DR to pretty much make your characters invincible to non-elemental damage for two rounds.