Thanks guys for the suggestions!

I'm still trying to teach him to bark on command, but strangely it's been a bit hard. Whenever he barks, I look at him and give the command, but then he would stop and look at me, trying to understand what I want. Must be patient I guess.
Criosphynx, I can understand why it's better not teaching how to train for protection on the internet, since such knowledge falling on the wrong hands (inexperienced owners) can be bad. In my case, I wouldn't want to do it with my pup, since I'm not having total control over him yet, so that teaching something dangerous is not a good idea for anyone's sake. Also, I want him to remain friendly and never develop any aggressive tendency towards anyone.
But well, actually my pup has scared a few people already, even thought he's friendly with everyone (and everyone just loves him). He has never been aggressive to anyone, but he barked to someone once or twice just coz the person was coming from the direction where some weird noise happened a few secs before he spotted him/her.
But well, maybe when he gets bigger, he will be more intimidating so that he could ward off dangerous guys.
But even so, actually I feel concerned about his safety too. Most people wouldn't go after someone with a big dog, but the few ones that does, they would probably attack the dog first, so that they could get the owner easier. So I would prefer to avoid confrontation as much as possible, whether my pup can fake aggression or actually really protecting me.
ruthcatrin, I live in Portugal, I'm not sure if pepper spray is legal, but it seems something soft compared to a weapon, and it's only for disabling someone temporarily, so that it might be fine to use.
About body language, I've tried to appear normal and not insecure, but I guess that I probably gave away a bit of my insecurity when I was going away. I guess that self defense classes are on my to-do list.