iCal allows you to create a backup file by selecting File > Back up iCal. You can later restore iCal by double-clicking the backup file. Restoring iCal from a backup works great as long as you have a recent backup. But that's rarely the case.
What if you could configure iCal to create backups automatically? You can, with a little help from AppleScript.
This script will backup iCal when run. You can create alarms in iCal to run scripts. To configure iCal to back itself up every day, create a repeating alarm in iCal that runs this script.