We never encourage doing this, but Armory encryption is about as good as it gets for these things. The key-stretching on your password is not only designed to make it expensive to crack passwords, it's actually designed to use tons of RAM so that GPUs have a much smaller advantage brute forcing them. GPUs will probably still be faster at password cracking than CPUs, but probably only 20x faster instead of 1000x.
On our website, we have posted a presentation I gave on security best practices. You might consider looking at slides 41 and 42:
http://media01.bitcoinarmory.com/InsideBitcoins_Present.pdfIt illustrates what key-stretching means, and shows some numbers for what kind of resources would be needed to break a password of a given length. And that's with default settings. If you are going to do this, I recommend that you use the advanced options when you create the wallet, to increase the RAM and compute time.
In conclusion, if you are going to do this, raise the advanced encryption settings, and use a strong password that is more than 12 characters. If you are not so concerned about physical security, write the password down and keep it somewhere that is accessible but not obvious. You really should only use this as a secondary backup method, to other unencrypted methods.
Though, I would still encourage you to skip this exercise and simply manage your backups with M-of-N. You can think of M as the security of the backup, and (N-M) as the redundancy (though I would argue that M=2 is nearly as good as M=3 or M=4--all of which are enormously better than M=1). The point is, you can use a high N-value to protect yourself from losing too many fragments.
Earthquake zones can do a lot of damage, but it's also not going to utterly destroy
everything in a 50 mile-radius. You can be comfortable that some of your fragments will survive if they are appropriately distributed. So something like 2-of-5 would probably suit you well.
