How to correct growling?

Contrary to popular belief, dogs are not *quite* so conceptually advanced to think that if you are punishing a growl you are punishing a behaviour that "might" happen in the future or "might" be lurking in the background. Besides, that doesn't really fly with the "dogs live in the moment" thing.

 It's simple, really. If you punish a growl, you are not changing the reason the dog is growling in the first place. And you aren't fixing the problem, and you are possiblt making the growling worse. And it's far more important to understand the reason for the growl so that you can fix the problem, and in turn the growling will disappear. Voila!

I would be mighty thankful that all you are getting is a growl and nothing has escalated!! It may never escalate, but it might at the same time. Clearly he feels uncomfortable about the presence of passing by - whether it be because he's been stepped on and feels vulnerable, or because he's guarding the space around him ("claiming space";). Whathever the reason, it is important enough to the dog to feel it needs to do that, and it's your job to teach him he no longer needs to defend, guard, or tell you off.