I think that a dog is a great theft deterrent, but only as long as you have the right dog breed (German Shepherd, Rottweiler, Doberman, Pit Bull, Boxer, Bullmastiff, Dogo Argentino, Staffordshire Bull Terrier, or Fila Brasileiro), the dog is accompanied with a good alarm system and home defense firearm and the dog is trained not to eat foods given by strangers so that he is not poisoned (this can be easily achieved with a shock collar training program). A good guard dog will not only alert you when there are intruders in the perimeter of your home, but it will also attack intruders when they invade your perimeter and will act as a deterrent to a home invasion. Just make sure that you take the necessary precautions for the safety of your children, the neighborhood children and the poor old mail man.
At my home in Costa Rica, I have a German Shepherd, an ADT Security System (sign at front door), a CCTV system with 5 cameras connected to my TV (front door, back door, front yard, back yard and garage), perimeter sensors in the back yard, reinforced entry doors and frames, Mul-T-Lock door locks (front and back doors), security window protection films on all windows, a 12 gauge Mossberg 590A1 shotgun loaded with 00 Buckshot and an HK 45 pistol loaded with Remington Golden Saber JHP. It may seem that I am paranoid, but as a matter of fact I did this when my wife's family had a VERY bad home invasion where the burglars came in, tied my sister in law and her grandmother and proceeded to loot the entire home. This opened my eyes to the fact that a home invasion can happen when you least expect it.