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The Cataclysm beta currently features a Requires Authenticator checkbox in the guild controls for each rank in a guild. Once activated for a rank, you cannot promote someone to that rank unless he or she is using an authenticator. At this time, the highest rank below Guild Master defaults to Requires Authenticator's being checked, and all other ranks default to its being off.

This is a much more reliable tool than making members show their Core Hound Pup in order to get guild bank privileges, which was really the only way to verify authenticator use before. Of course, this is the beta, and that means the functionality may change drastically before making it to live, if it does. I predict, however, that Blizzard will try its very best to release this setting, as its use should reduce time spent recovering stolen bank items.

Source: Link

dont you have to pay for that though?

Yeah you do have to pay for it but it is really cheap and worth it.

Well, technically, you only have to pay for a tangible authenticator. There are mobile phone apps that also serve as authenticators that are free. I bought my tangible authenticator for $6.50 years ago. I doubt the price has changed. As someone mentioned, the peace of mind is worth it.

The peace of mind while you're stealing from the guild museum is definitely worth it.