I have been training my female in Schutzhund. She is almost ready for a SchH 1. She recently bit a man who asked to pet her. What did I do wrong?

Hey Ed,

First I want to say you have a great site and I value your opinion very much. I have a concern with my 5 yr. old female GSD. She is schutzhund trained although not yet titled. I will admit that I am still a novice trainer/handler even after a couple of years doing this work. My GSD recently bit someone for the first time. This dog has german working lines, father was 2 times BSP participant, and etc. She has had both defense training and of course prey. Some times I have felt she may be a little to defensive other times I have felt like she was locked in prey. I emailed you sometime back about her character and you suggested I only work her in prey drive. That is what I have been doing - really I haven't worked her much lately though. Anyways, I was at a place where you can take your pets inside. A rather large man asked if he could pet my dog. Normally this is not a problem. He approached her slowly and stuck his hand out towards her. He was looking her in the face the whole time. She sniffed his hand and her ears even went back. He then rubbed her snout and brought his hand back in front of her nose to smell again. At that point she snapped his hand, took a small chunk out of it, and began a defensive bark(I was holding her back at this point). I immediately corrected her HARD with the prong collar and told her NO. She stopped. So, What happened here? I feel as a trainer/handler you will always have some responsibility in what your dog does. What have I done wrong? Any advice would be appreciated.

Thanks,
Mark