Another option is to make a CLONE of your hard drive, not really a "backup" in the usual sense. A clone is a complete and exact copy of your entire disk. However, unlike good backup software, you cannot easily update a clone to reflect recent changes. Your only choice is to completely re-make the clone which takes time and really should NOT be done in the background while you're doing other tasks.
Geofelt suggested this when he / she said "Acronis True Image". As an alternative to the free trial Geofelt mentioned, go to the WD website and download / install their free package called Acronis True Image WD Edition. It is a free version of Acronis, customized and limited on one important way. It will only make a clone TO a WD disk. So, making a clone to your WD external will work. BUT if you ever have to recover and must try to clone BACK to your main internal HDD, that would only work IF that drive also is by WD. If that is NOT your case, get the Acronis free trial version that is not limited in that way.
Using cloning software in place of backup software has another problem you should recognize. In the event of main HDD failure, you may not have an OS to boot to. Somehow you need to be able to boot the machine and run the cloning software to completely restore your HDD. You have to figure how to do that. This is not so very different from regular Backup systems, but it's still an issue you should plan.