If you have encrypted columns in a database or certificates used to create them, you need to make sure that you back up the Database Master Key as part of your maintenance, and then protect that backup file. Here's the short version of the command:
BACKUP MASTER KEY
TO FILE = '<complete path and filename>'
ENCRYPTION BY PASSWORD = '<password>' ;
And here's the BOL link for that: http://msdn.microsoft.com/en-us/library/aa337546(SQL.90).aspx