Availability comment expiration date

The Availability Comments field on the employee profiles is very useful when calling out crews, as this shows any notes we need to be aware of when previewing a callout.  We often have notes to consider, and we would like to start using this field, however, the nature of our comments due expire.  It would be nice to have an expiration date for this field, and an option for no expiration.  Otherwise we have to remember to go back in and remove the comment, which if we don't, can leave to confusion.