Dogs have been used as a main component of security from thousands of years ago and today they go hand in hand with home security signs. Chinese palaces have been protected by dogs. Greek mythology has Cerebus standing guard over the gates of Hades. Dog breeds have very distinct personality and behavioral traits. Some dogs are loyal, protective or have other characteristics that make them qualified for guard dog roles. Home security signs on the perimeter of your property that warn of guard dogs are a great first layer of home security for the simple fact that they make a criminal think and wonder about the difficulty of stealing from a home with dogs.
Most people have some familiarity with the pictures of Doberman Pinscher or German Shepherd breeds as guard dogs. These particular breeds do make superb guard dogs, especially when properly trained. They possess the physical size, and personality to protect anyone's property. Other breeds such as Bull Mastiffs and Rottweilers possess excellent guard dog capabilities as well.
I know from personal experience that German Shepherds and others can be taught to discriminate between those who are allowed in the home and those who are not. I house sat for some friends of mine one time and they had a huge German Shepard named Samson. When I first went to their house, my friend Ken took me out to meet Samson and told him, "Samson, this is our friend Tom." Samson and I were best friends from then on through the rest of the summer while his owners were away. These dogs operate by sight and smell. They will readily recognize not only family members but 'authorized' visitors as well. Family friends will be welcomed with a friendly tail wag; Strangers get a stare and a warning growl. If a stranger comes closer, especially to a family member watch out. A nasty bite or more will come about if they persist.
Even though dogs can be destroyed by a gun or poison, most criminals are not going to go that far. Most of the time, just having home security signs warning of guard dogs will make a burglar reconsider. They really want an easier target of which there are many. Dogs with the physical size and presence of the breeds mentioned are, at least psychologically, a threat most burglars do not want to deal with, which increases your property security.
Although larger dogs may be optimal, much smaller breeds can make excellent guard dogs too. They just need proper training.
Having a dog that constantly barks at everything is not the answer to any successful security issues. With the owner consistently ignoring all the warnings, the burglars will realize that they do not need to be nervous. Most breeds just need some good training to solve barking problems and false alarms.
It is best to have a dog that has both inside and outside access. Dogs that are allowed access to both will consistently cover the whole property. This can be accomplished with an appropriate sized doggie door. Not one so large that it makes home invasion easy though. The right sized doggie door will allow most dog's access to the outdoors for bathroom breaks and patrol duty. With a little thought, the door can be made big enough for the dog, but small enough so most men will not have access.
You should complete your guard dog program by placing home security signs warning about the guard dog in places that people can see day or night. These are considered clear advertising 'that your property has guard dog security. Criminals do not need to see the dog to reconsider there illegal activities in regards to your house. Proper signage will alert them to the fact that one encounter will be more than they want.