My is first line of defense is an 85 lb. akita . She doesn't bark unless there is someone there. Even if she sees the person on a pretty regular basis (pool guy), she will still bark unless we tell her it is okay. If we introduce her to our friends, she usually does not bark at them the next time she sees them. If Chris thinks he can feed my dog and befriend her, he had better have some very good medical insurance. Akita are very tough dogs and were used as impreial guard dogs by the Japanese. They were also used for hunting bears. Her sense of hearing, scent, and night vision is far superior to mine so I would say I trust her as my first line of defense. I know dogs can be shot or poisoned, but unless my dog is shot from a distance, she will most likely alert us first. If she does get taken out, I'm going after the SOB that did it.
To back her up, I have an alarm system that we set every night. It is hard wired instead of wireless so the signal cananot be jammed. We have cellular backup if the phone lines are cut and like most systems, it has a back up battery if the power is cut.
For the final line of defense, I am one of those "forget the dog, beware of owner" kind of guys. I keep my Sig P229 next to my side while the wifie has the Ruger GP-100 on her side. I also have my Surefire 6P with the 120 lumen lamp on the night stand and a shotgun in the closet just in case.