It comes more natural to some breeds than others.
Saying that, a natural guard male german shepherd I had a few years ago was so people friendly that we stopped the window cleaner coming as he always brought different young lads from a not so good area. They would put their arms through the window to pet him. He never barked at a knock in all his 7 years.
He was trained to bark on command for trials competitions and I think this helps.
Murphy will probably start protecting his territory naturally as he matures, which is probably nearer a year old for his breeding. He is a bit young yet, just hitting lower end of his teens so there are too many exciting things to think about without worrying about keeping strangers away

One word of warning. Teach the command 'quiet' BEFORE teaching him to bark or you can end up with a noisy dog

very easy to do. Just say the command when he is looking at you without making a noise. Then praise him.