if it was my dog and had NEVER shown aggression before then I would have to look to why the change, it could be the dog is in pain or has a brain tumor that could be treated, but before I had the dog PTS I would certainly have test to determine if there was an underlying problem, and then make the decision (if I am able to) to have the dog PTS or not.

mo

My Nan had a fantastic Airedale, he was as placid as could be, good with other dogs, people, babies etc... one day he just turned, he went to the vets to see what was wrong with him, it turned out he had an inoperable brain tumour and had to be pts So sad... if my dogs just turned I would want to find out why, as I always think there must be a cause, either clinical, pyschologically or enviromentally....

we had a black cocker who adored my hubby, but little else and flew into a madness for no reason, the final straw was she bit my sister in law and would leap at any visitors - we had four small children living near us and could not risk the gate being left open - afraid went to the doggy kennel in the sky.
we now have labs

When I lived in South Africa our German Shepherds were first and foremost our pets, but also played an important role in protecting us. We had 8 foot fencing all around our property, with signs every 6 feet warning of dangerous dogs. Some neighbours of ours had a barbeque one day, got a bit drunk and decided it might be fun to climb our fence and go paddling about in the river at the bottom of our property - we were out at the time. On the way down the shepherds were barking quite viciously so they picked up sticks to ward them off - that was like waving a red flag at a herd of bulls One of the dogs attacked one guy and bit him on the arm, quite badly so we were informed by the police, to the extent he needed surgery to repair the damage.

We came home to blood all over our doorstep (why was he at the back door???) and the police waiting for us, too scared to go in. After checking out our property, with all the warning signs,locked gate etc, we were asked if we wanted to counter sue for trespass. There was never any mention that the dog would have to be put to sleep. We knew he wasn't good with strangers, so when we had visitors he was locked in a spare room in the house so he couldn't bite anyone. With the family he was a wonderful and faithful companion who's tail never stopped wagging. After that awful day whenever we went out he was locked in the house, just in case.

I would probably feel differently now that I have kids. But in those days my hubby worked away from home a lot so I was left at home by myself, on 5 acres of land with neighbours who probably wouldn't hear any commotion. We took all necessary steps to ensure our dogs wouldn't get out, and people thinking about coming in would see all the signs, including one on the gate saying beep, don't come in, vicious dogs running free. Janus used to sleep in my bedroom next to the bed and I can honestly say I never once felt nervous or worried about intruders with him by my side.