This excellent advice comes with acknowledgments to Gizmo's Freeware at:
http://www.techsupportalert.com/
"If you're backing up to an external USB drive that's connected to your main PC, a disaster such as a fire, flood or theft could easily deprive you of both your main machine and the backup.
"When you're planning a backup regime, choice of software isn't as important as choice of storage location. Off-site, or at least a drive that you take away from your house (or small-business office) once the backup is complete, is always the way to go."