That will work. Or you could right click on the game in your Steam game list and click on properties - updates, then choose the option to not update the game.
Hi,
That suggestion doesn't work. The "don't update me" option is designed so that games you don't currently play / won't again don't get updated needlessly. The moment you launch a Steam game in online mode where there's an update available Steam will try to update regardless.
The safest thing is to simply stay in Offline Mode, however that's not useful if there are other Steam titles you play that require you to be online - multiplayer stuff for example.
Personally, I will stay in Offline mode until I chose to patch as I'm only playing Skyrim at the moment.
Cheers,
Scoob.