Has he had a full veterinary work up to be sure that there is nothing going on physically? Pain can lead to aggressive behavior. If he checks out medically then you really should consult with a professional who can see him in person and work with you to develop a plan to help him with these situations.
Typically behavior such as this is not typically a "sudden" thing as much as we would like to think so. Unless there is a medical reason, I would suggest that you think back and see if you can pin point when you might have seen the first behavior and you might have just brushed it off… You say that the litter brothers/sisters do not show any of this behavior? Do you see them regularly? Do you know the owners? Have you talked to the owners of the litter brothers/sisters?
I would agree that you should seek a professional to witness the situation in person and give you possible solutions. This is of course once you have ruled out anything medical, especially and Thyroid issues.
I would agree that you should seek a professional to witness the situation in person and give you possible solutions. This is of course once you have ruled out anything medical, especially and Thyroid issues.
this is really of great importance because there may be something that is happening that you and others are missing. Of course a complete vet check is in order. Tell your vet about the behavior issues. Also I'd ask if the vet knows of any behavioral vets. Also, i'd suggest doing lots of obedience with this dog. clicker training is wonderful. also read Control Unleashed (pay close attention to the off-switch game and look at that). And google Overall's Relaxation Protocol. Start doing this yesterday. CU and the RP will help with impulse control. I don't think that is the entire problem with this dog, but it is probably part of the solution. AND I feel confident in suggesting this without even seeing the dog and it should be compatible with anything a good positive behaviorist would give you to do.
In the mean time, I'd contain him when people come over especially if you're not there. Do not think of this as punishment, but rather helping him cope with things that he is not prepared to cope with.
I've had some of the same issues with my Guppy. The DAY he turned 14 months he turned into Mr. Grumpy Pants. Resource guarding etc. I had it under control and then we moved across country and are staying with a friend (a friend who doesn't like dogs and is narrow-minded when it comes to behavior-her suggestion is for me to "spank" my dogs….yeah right). Guppy doesn't like my friend we are staying with (her fault) and his behavior has sort of relapsed back to Mr. Grumpy Pants. I control it as much as possible (first growl gets him kicked off the bed) but until we are all settled into our own place I suspect I will have to ride it out.
Ruling out anything physical or a sickness or something should be done first. But I have seen this in my female. There are two people (friends of ours) that she absolutely will not have anything to do with. They have two dogs of their own. They are wonderful people, will do anything for their dogs. They come to the house and she will growl and snap at them. They have never done anything to her. We have had them over for BBQ's and been sitting by the fire in the back yard. She will be wandering around but will not go near them. If they get too close to her she snaps. There is no reason for it, she just does it. Those are the only two people who she truly hates.
While I certainly understand resourse guarding, I disagree that it happens "one day". There are typically signs and most of us, many of us, miss those signs or ignore them.
Sometimes a dog takes a dislike to someone, either because of some action on their part, or just because of circumstances. I became "persona non grata" with my friend's stud dog (who had previously been fine with me) when I visited her with the smell of my newly acquired male Basenji on my clothes. Her dog was currently breeding a visiting bitch, and perhaps the smell set him off, but from that day on he did not like me. I avoided confrontation by assiduously refraining from looking him in the eyes and avoiding any other behaviour he could take exception to. He outweighed me by about ten pounds, and I wasn't about to test her control of him! 
Our relationships (hers & mine, mine & his) survived, but I had no indication he had revised his opinion of me over time, although I mounted a "charm offensive" and brought him biscuits. He would take the treats from me, but barely tolerated my presence. Once a dog has made up his mind about someone, it can be difficult to change it.
I have had dogs take a dislike to someone. And that's okay. Aggression toward them is not tolerated. I can only agree with others– full vet check, thyroid check and then you need to consider talking to the other OWNERS, not just the breeder, and people who have owned from the line before-- and then consider a behavior specialist if you need it because this behavior is escalating.
I agree with previous posters your dog needs veterinary attention to make sure that ther's not a physical reason. Then all being well it's agood idea to obtain professional behaviourist help.
In my opinion you shouldn't be showing him like this - even though this aggression seems to be against certain individuals there could be a time when he takes against the judge.
In my opinion you shouldn't be showing him like this - even though this aggression seems to be against certain individuals there could be a time when he takes against the judge.
Yes, getting kicked out of the ring because your dog growls and won't stand still for the judge is very very embarrasing!! This did not happen to me with a B but the Shiba Inu we had. I was 16, it was her first show and she growled at the judge and would not stand still on the table…...I got excused from the ring.....in my hometown.....and its a small little show, 175 dogs. After that show we got her spayed, as I did not want to carry on that temperment in puppies. She was a very good dog but I am glad we spayed her because she had an attitude! She was my first show dog and we did not do proper research on the breeder first. Sorry, this is getting off topic.
