Ex-cons who now do public service teaching people what burglars avoid most during robberies list DOGS as #1.
I can confirm that this is true! Every criminology course I've ever audited showed that criminals will actively avoid homes with dogs. Unless you have a stockpile of gold or something someone REALLY wants, you will not be randomly victimized if there's a dog in your home.
Oftentimes burglars will case neighborhoods before making their move. If they see you have a dog, and esp. if it's over 50 lb., they will move along. This is discussed and proven in almost every entry-level criminology course.