how to deal with a dragons high attack roll

[TuggyNE]

Druid has Enhancement to your existing natural armor bonus spells (barkskin is one, I think), in addition to enhancement bonus to natural armor. So a +5 barkskin and another nat armor +5 spell is +10. Upgrade items for a few more, an animated +1 heavy shield is another 4 AC (screw mithral, this one doesn't even touch that casters arm!)

For what it's worth, while AC pumping is a valid tactic (that requires, generally, moderate to significant investment for most characters), these suggestions aren't so great. Enhancement bonuses to natural armor do not stack with themselves, and animated shields explicitly still have ASF and ACP just as normal. Alter self or polymorph into something with high NA is a good base for then barkskinning it, though. Further effort depends on getting deflection and armor bonuses (such as (greater) luminous armor for casters), and maybe stacking up other miscellaneous boosts like defending weapons.