Protecting the Spellbook

[Buri]

The recent "What is the point of Spellbooks" thread got me perusing the wizard spell list to see what one could use to play up the game of protecting the key to your power. While there are certainly some spells of the "that could come in handy" variety nothing really jumped out at me that fills this role. So now I'm curious how do you guys protect your tomes. What kind of setups do you have to ensure your secrets aren't gone for good?

[EWHM]

Buri,
Here are what my players use:
Fire traps and the like on the item itself, sometimes the old sepia snake sigil. Usually it's kept in a handy haversack or the like (the copy you're using).
No less than one backup copy of the spellbook, kept in a secure and usually secret location
A reciprocal agreement with at least one other wizard to assist them, let them memorize from your book, etc in the event of a loss of a spellbook. PCs and close allies will almost always agree to this pact with just the reciprocity as inducement. NPCs usually require a bit more cultivation.

The more paranoid of my players keep more than one backup, and keep strategic caches of scrolls at various places also. I run a pretty simulationist ship though, so I'm not representative of the typical GM you'll encounter. I'll pretty much never go after your spellbook for gamist or narrativist reasons, but if the natural or perceived interests of NPCs running in a simulationist manner aim at your spellbook, well, them's the breaks. In a like vein, my NPCs never use things like sunder or the like for gamist/narrativist reasons (i.e. because the GM wants to destroy item X). Instead they use sunder and the like pretty much in exactly the same circumstances the more ruthless PCs would, when they perceive that sundering item X really is their best tactical option outweighing their concern for destroying part of the treasure.

[Grimmy]

There is a bookmark in ultimate equipment that makes your spellbook appear to be a boring book about bird watching or stamp-collecting, and it gives your book non-detection.

[Lord Pendragon]

I've never had--or been--a DM that targets spellbooks. Though I suppose if I were I'd go for a Blessed Book or the book Grimmy mentioned.

[Vincent Takeda]

I like to put all of my spells into travelling spellbooks, and I count those as my 'main books' they have no protections on them and they're thin and tucked away in the satchel of not necessarily my wizard but the member of the party who is least likely to be successfully stolen from. Then I'lll take one of the ornate full blown spell books that we've looted from our enemies and wear it unsafely and easy to get to on the wizards person.

If someone wants to steal a spellbook, give them something to take that you dont mind them taking. Even better go buy a fancy ornate spellbook to wear openly and easy to steal, but never put a single spell in it. Somebody just got away with an empty spellbook!

Way to go!