Aussie recent agression

Question
I have a 10 month old male neutered Aussie who has always been friendly. We take him camping with us and two weeks ago a man dressed in cameo with a beard  came up out of the creek behind our camper where we were sitting. He immediately started barking and growling and we could not get thru to him to stop, ir was like he was in a frenzy. He had been very friendly all week with other campers and their dogs, but something with this guy set him off. Then last week i took him to Petsmart where he was again friendly until a man with a beard attempted to pet him, again same reaction, last night he jumped at the TV screen, same scenario. This dog has been socialized from 9 weeks on, I take him everywhere with me for that very reason to get him out and socialize him. I am now hesitant thinking if he bites he will do it too quickly for me to step in and stop him. He is fine with my self and my husband, typical velcro Aussie, no aggression issues. We have a farm and he has been working our stock since he he was about 6 months old, and does a great job. Any suggestions?

Answer
My suggestion is that you get an appointment with a behavior professional who can instruct you in some counter-conditioning and desensitization techniques, so that you can attempt to change your dog's mind about people with beards, or people who strike him as strange.  Unfortunately, Aussies can be prone to regard strangers with suspicion, and some never will accept strangers that seem odd to them.  Also, I don't know your dog's socialization history, but even if it was very thorough, this is still a trait that affects some dogs, mostly from working lines.  I have a dog like this, and when I take her in public I either have a Gentle Leader or a muzzle on her.  Not that she doesn't have great bite inhibition, but she is a "poker" and when she pokes, her nose feels hard enough that some people would swear she bit them, so I protect her from harm by taking those precautions.  I always err on the side of protecting my dog.  I hope you will too, and I hope this is just a case of adolescent fear that a behaviorist or experienced positive trainer can coach you through.