I'm so sorry you are having such a sad and difficult time. I went through a somewhat similar problem a year ago. Ripley, the litermate of my nearly 6-year-old Pyr, Sophia, bite me 3 times...once quite badly..in a 3-week period. I worked with Patricia McConnell, a nationally known animal behaviorist (author of "The Other End of the Leash") as well as with a local behaviorist. Additionally, my vet put him on Prozac, in case there was some kind of imbalance. This went on for over 2 months,...with me fearing each day that he might attack someone else. He had always been "Mommy's boy". He was Puppy #5 from the one litter I had (under the guidance of a long-time Pyr breeder), and we bonded from day 1. Of course, we all speculated that he might have a brain tumor, but decided not to do a CAT scan as after spending the approx. $1,300.00, to check it out...if he did have one, there really weren't any practical options. Believe Me....money never comes into play with my dogs if $$$ can fix the problem. On top of the health ins. I have carried on all my dogs for the past 20 years, I have willingly spent thousands of dollars to give them the best possible quality of life. Then one morning, I realized that there was a look in his eye that fightened me. Plus his behavior was a little "off". But, as someone who always wants to give her beloved pets every possible chance, before I made the "final decision", I called a long-time, highly respected Pyr breeder to get her opinion. She guided me to the choice I knew was necessary, and my wonderful vet came over to my house that evening to perform the sad task. (Of course, like all of my deceased beloved dogs, he was creamated and his ashes have a place of honor in my bedroom.) Like someone else mentioned in a previous response, one always must consider the quality of life possible for dogs who have physical or behavioral problems. And, of course, risk to self, and others must factor in. Dogs know yesterday and today, they do not know tomorrow, and...a peaceful death by euthansea is sometimes the kindest and most loving thing we can do for them. My thoughts and best wishes are with you and Petra.