Chaining makes dogs aggressive, not protective.
Protective dog: Accustomed to people and can tell when family is being threatened. Learns to be protective by interacting with family
Inside, family pets make the best guard dogs. Just ask a K9 officer. Most K9 officers keep their dogs inside the house where they are considered part of the family.
Guard Dog Issue
How can a chained dog stop an intruder? All he can do is bark.
Leaving a dog on a chain and ignoring him is how to raise an aggressive dog.

Aggressive dog: Can't distinguish between family friend and threatening person. Will attack anyone - children who wander into yard, policeman, the meter reader
Statistics show that inside dogs are very effective way to scare off intruders