Neapolitan mastiff natural protection ?

i have a neapolitan mastiff and i was considering to train him for personal protection but i have read that no protection is needed since thy are natural but how can i make sure that when i am in a REAL danger the dog wont back off when my dog sees stranger he barks very hard as if he is going to eat them i have not brought a decoy for making sure please help me I ALSO HAVE A HARD TIME TRAINING HIM TO BARK ON COMMAND ALTHOUGH HE BARKS AT STANGERS I TRIED THE TOY METHOD AND REWARDING HIM WHEN HE BARKS AT THINGS THAT PROVOKE THEM thanks in advance guys !! i will choose as a best answer folks! :)