Try a robot, if you are not prepared to put work into an animal I strongly suggest you DON'T get one.
But if you must, get a older dog, not a puppy, many breeders have older dogs for sell.
Look for the guarding breeds, Rottweilers, German shepherds, Akita, Mastiffs, Doberman, Malamute , Great Dane or Hungarian Vizsla.
Also Greyhounds are great guard dogs and very lazy low maintance.
I warn you all dogs can be aggressive if trained.