The Knights of Dusk

[The Black Sun]

Best anti-xray trick:
X-ray texture packs can only see blocks touching air so simply surround your chests with blocks.
X-ray client mods are a little more difficult. The best way to protect a chest is to surround it with an ore that the mod does not turn invisible and that an xrayer isn't going to go out of their way to find (such as iron ore).