Guard dogs have been used for many years to protect alsorts of properties. The main reason they are there is to act as a deterrent more than anything else and any potential burgler is going to opt to try and break in to a property that's unguarded rather than the one with the alsations patrolling outside. If a break in does occur, then rather than the dogs being there to attack the intruders, I think they're there more as a source of noise and its that what will draw attention to what's going on.
With technology advancing as fast as it is these days, and with nearly all businesses having alarms and CCTV operating, maybe soon we will see the guard dog not being used as much, but in a residential property, they're still a good deterrent to have. If your family pet is also protecting your home and family, and you're making sure you look after them properly, then I don't see that there's anything wrong with that.
