Use a large external hard drive both as installation media and backup drive

Another possible option: use rsync and a launchd job to execute it when the disk is mounted. I believe Time Machine uses a similar approach to running on disk mount. For the hourly execution, you can use cron. The discreet notification can be done in a number of ways (for instance sending a mail or the Growl extension which allows notifications to be sent from the command line). killall rsync should stop the backup safely if you need to pack up and go. Also rsync is also entirely capable of networked syncing.

It will take a bit of work to set up, but the advantages are:

• it's versatile (see man rsync, they pretty much thought of everything)
• it's discreet
• it doesn't cost anything
• rsync is quick

You may find this helpful for launchd jobs involving disk mounting.

Edit: I should add that the --partial option to rsync will mean that the backup is resumed after killall rsync.

Edit 2: You can use a Control Plane context instead of launchd if you prefer.

In Mountain Lion and greater, you can create multiple separate backup disks with Time Machine. Get an USB external HD for traveling, and use that to backup your Mac whilst on the road. When at home, you can do a backup to another HD, (USB or otherwise,) which stays there permanently. I take this external HD when I travel. It is wicked fast, and demonstrably rugged, as I have dropped it several times with no ill effects. You can also use this disk to make a CCC clone, if that is your preferred backup method.

Note: It is not a wise idea to have a backup partition, (CCC, TM or otherwise,) on the same drive you're backing up. If the HD itself goes poof, you've lost the backups you need to restore your system.