Most dogs make good deterrents. If you're a random target and the scumbag sees big piles of shit and a heavy cable in the yard, they're less likely to intrude on your home with their scum-fuckery. Dogs also make a great alarm if they are somewhat trained, giving you time to arm yourself as previously stated. Finally if a dog is especially territorial or aggressive or if he has been trained specifically to protect the home from strangers that you did not show him you approve of, a dog will die defending your home. My dog is just a companion and might be a deterrent or alert but I don't expect him to try and protect my home.