My cavachon just turned 9, and she has been the best family dog ever. My husband and I are so attached to her and we have had 7 grandkids in the time we have owned Lucy. She has always been a little aggressive toward the mailman and UPS trucks and delivery men. She will bark and jump up on the door or screen. Throughout the years off and on, she has ran from the front yard to go after people, bark at them in an aggressive way. When we would get her, she would come to us right away and be her happy self, wagging her tail. We thought it was very odd behavior, but because she was always so happy, loved the kids no matter what they did to her, it didn't concern us too much. About 2 years ago, my daughter was walking her and she got away from her going after somebody walking, jumped on the person and snapped at her but missed. After that, we had in-home training, private lessons which cost us a lot of money, but we felt it was worth it just to be safe. She then became a therapy dog because the trainer loved her and said she had such a sweet disposition. She passed the test, and all was well, until last week. My husband was walking her on a leash and our neighbor walked up to them, talked for a minute, and when he was walking away, Lucy jumped on him, barked aggressively and bit him in the leg. I am now so upset, depressed and just don't know what to do. I got a muzzle and we will not let her out now without it, but I still just don't understand how this can happen to a dog that is 99% completely friendly, sweet, and generally quiet and docile. Even the groomers and boarders tell us that she is one of the sweetest dogs in the group when they have her. So my vet tells me since she has spaniel in her, to do as much research as I can regarding cocker rage. It appears that some mixes that have any spaniel whatsoever can just suddenly turn, even on their owners. Does anybody else know anything about this? I love my little Lucy so much and can't imagine having to give her up, but at the same time, I have always said that I will never keep a dog that bites. Here I am, faced with the truth of my own words and I don't know what to do.

 

Good advice from the others. A few tips (I have two shy puppies):
- A good way to measure if your dog is over threshold is if she is taking treats and how. If she is not interested, she is over threshold and not learning anything (rather just getting more scared), so get her out of that situation. If she is taking it but in a snappy, bitty kind of way, she might be too nervous and you might want to increase distance or get her away from whatever is scary. If you pay attention, you'll soon be pretty good at measuring your dogs level of fear just by how it feels when she takes the treat.
- I try to not use treats to distract the dog (I do sometimes though, when the scary things just shows up suddenly at close distance). What I try to do is to reward the dog with treat when he is looking at the scary (or exciting+scary) thing, but at a distance where things are still under control. What I want to achieve is my dogs reaction is to look at me "hey, there is man with a hat approaching, where is my treat?" instead of "oh my god, man with hat, we will all die, we need to run!".
- When it comes working with shy dogs, our own lack of patience, greed for progress and frustration is a major obstacle. It's easy to want to "fix" things and go too fast and instead making things worse. Go slow.

I could write a book about this Hopefully it's just a normal fear period, and she'll be back to a normal confident state soon.

 

I don't know what a cavachon is, but the behaviour you're describing is disturbing...

I would start with a vet visit.. Something could be bothering her.. Get full bloods including thyroid panel, as well as a general health check...