how to deal with a dragons high attack roll

[Immabozo]

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.

True, enhancement bonuses do not stack, but a wording peculiar to some of the druid +NA spells is that it is "An enhancement bonus, to your existing natural armor bonus" now, unless I wildly misunderstand the wording, I believe that is an enhancement bonus, to an enhancement bonus, making the two "stack"

Not that this is game breaking, nor is it cheese (might be a little pedantic, on the scale of cheese, this isn't even that orange plastic "cheese" they call American cheese, the ones in the peel-able plastic wrappers we got in our lunches as kids), I think you can get a +8 enhancement to NA and a +5 enhancement bonus, to the NA enhancement bonus.

But in the game of stacking AC, there is a good large difference between 35 and 40.

I didn't know that about the shield keeping the ASF, thanks for correcting me.

EDIT: On second thought (a brand new player vs a, now, year and a half experienced player) doubts what I said now and would not be surprised to be wrong.