Seems to me the originator did not give us a complete enough story.
A dog growling is not an attack. It may just be a warning to stay away. So if a person tells you to stay away do you think it's okay to shoot him?
The rule of thumb to remember when employing deadly force is a reasonable fear that your life is in danger. A dog's growl, while menacing and perhaps scary sounding, is not, by itself, a deadly threat. That being said, if I saw a scary looking dog (such as a Doberman or a Rottweiler) growling at me, I would definitely draw my weapon in case he decides to charge.
Best bet is to check with local law on the matter.
Just this past summer I was walking my 5 month old German Wirehair and things were good.
Up the block I saw a woman, her child and thier Palmerainian ( spelling sucks.. Small Dog looks like a dust mop ) They were playing in the yard.
3 Pa. C.S. § 501, KILLING DOGS; DOGS AS NUISANCES
(a) LEGAL TO KILL CERTAIN DOGS - Any person may kill any dog which he sees in the act of pursuing or wounding or killing any domestic animal, wounding or killing other dogs, cats or household pets, or pursuing, wounding or attacking human beings, whether or not such a dog bears the license tag required by the provisions of this act. There shall be no liability on such persons in damages or otherwise for such killing.
First a growling animal is not necessarily an attacking animal.
When I took my CCWL class the instructor gave a specific example which covers this type of situation.
A guy was hiking in a wooded area when two dogs came over a hill growling and fussing, but not actually attacking. The guy fired simply to scare them away, not to kill them. Seconds later the dogs owner came over the hill raising holy hell and called the police.
I don't remember any further details except that the gun owner lost his license.
My conclusion is that you better either have bite marks or some witnesses because otherwise it's your word against his.