Any advice on a junk yard dog:?

This response is based on a life time of working, training, and living with animals. Based on experience, I can trust the animals I have trained when I am in control. When I am not in the vicinity I cannot predict how they would react.

The liability of guard dogs is beyond what I can accept. My recommendation would be security cameras with app access on your cell phone. Second line of defense would include electric fence used to contain livestock. It will not injure an invader but would give them a warm feeling all over. Thirdly family dogs that warn you of an intrusion of your personal space. Smaller dogs will exhibit their dominance quicker because they are scared. The last line of defense for your partner may offend some, but oh well. A shot gun loaded with buck salt in the barrel, #8 buck shot for the second shot, a slug for the third shot, and # 2 shot for the forth and remaining shots to protect his family.

Another idea is a sign stating that you believe in the second amendment, but my neighbors do not.

Summary: Do not depend on dogs to protect your property, depend on yourself.