how to deal with a dragons high attack roll

[TuggyNE]

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"

It's an enhancement bonus to a natural armor bonus. No more, no less. Just like the amulet of natural armor.

So far as I know, there are no enhancement bonuses to enhancement bonuses; the system simply does not use that level of indirection.