Puppy Barks and Growls at Strangers

Question
Hi Susan,
 My situation is this:
I have a Boxer/Black Lab mix puppy, Nina, that I have raised from approximatley 5 weeks old. Nina is now 7 months and about a month and a half ago she started barking and growling at virtually everbody that is not me, or my girlfriend, including other dogs. When i take her on walks she will bark and growl at people (and other leashed dogs) as they walk by. If they are brave enough to stop and pet her, she relaxes almost immediatley and will proceed to lick them to death.  Same with dogs, she goes to the dog park and to doggy daycare all the time and gets along great with every kind of dog; but if she is on the leash or she is kept from being able to meet them face to face (like if they walk by us while we are on the front porch or walk past on a leash while I am walking her on a leash)she will bark and growl until they are out of sight.
If i walk her in a highly populated area, where there are many people walking by,  she acts fine. But if it's just a few random people walking by; or if my nieghbors come home or walk by,  she goes crazy.  
 Any suggestions you have would be greatly appreciated. I want everyone else to get to experience the sweet and loving dog that I know, and not to be afraid that she will bark and growl at them.  Thanks for your time.
Oh, and she was just spayed yesterday.
 Sincerely,
Sean

Answer
Hi Sean, It sounds like she is thinking that she must protect you and her property. Which is normal at her age. She is at a perfect age to learn. Teach her a hand signal and voice command that tells her it is okay not to bark. I let my dogs bark once or twice at strangers, touch two fingers to my neck and say, "It's okay, back to me." At first she may not get it, and you may have to say firmly, "LEAVE IT". and call her back or put her on a long line and reel her back in. Eventually she will check with you and if you place two fingers (like the peace sign) on your neck, that will be enough for her to come back to you and stop barking. Doggie parks and some doggie day cares can be bad because the dogs are not well trained and your dog can pick up bad habits. But many are okay. Take her to pet supermarkets, walks...and make her sit quietly by your side as people and dogs walk by to test and train her.  Please leave me some feedback, nominations if you wish, and keep me posted. The only way we can tell we are doing a good job as volunteers is by your feedback or reposting us. It is much easier to see results in our classes, and we can correct problems so much easier. Be sure to let me know how it goes with her and you as soon as you can. Thank you for writing. Regards, Susan