Used Temple Reccomend Book Disposal

My bishop asked today about disposing of the temple recommend books after they are all used. Meaning the book of carbon copies (with no recommends left to give out).

He was wondering how long he is supposed to keep it, and how it should be disposed of (shred, fire, etc)

Is there any guidance on this out there? If not I figure we will keep them for 2 years then shred them.

They should be retained until the last issued Recommend has expired.

Dispose of them in a secure way, that is most practical for you.