A little background...

 About 5 years ago we rescued a Rottie/Shepherd mix who was about 3 years old at the time. He was found on the road after having been hit by a car. We had 3 other dogs and all was well for a while. Once day about 1 year or so after we got him, he and our border collie were in the fenced in back yard when another dog came walking down the street on a leash with owner. Both our dogs started barking and then the Rottie just turned and started attacking the border collie. He had the border collie down on his back and then just started thrashing him around like a rag doll, even though the border collie was submitting and not able to do anything back. I screamed for him to stop and release but nothing. The border collie was screaming, so I took a broom and started hitting the Rottie to get him to let go. Finally after about 5-6 times, he let him go. The border collie was severely injured with puncture wounds to the neck and had to have surgery.

 We almost decided to get rid of him then. But we opeted to take the Rottie to the behaviorists at the UGA vet school. We worked with him, had him on anxiety medication, and kept those two dogs separated almost all the time. Things were ok for a while, about 3 years. Then last week, the two dogs were outside again, same scenario, and again the Rottie attacked the border collie. Puncture wounds again, but no surgery was needed.But again, it took almost 10 times of hitting the Rottie with a broom to get him off the border collie.

This is a dog that gets so anxious and aggressive, that he is almost impossible to muzzle, and we've only been able to get him to the vet twice to have vacinations. And both times he had to have lost of sedatives before the vet could approach him.

 We have 3 other dogs whose safety we are obviously concerned about. But more than that, we have two toddlers we are even more conerened about. The Rottie has never been aggressive towards whem, but we have NEVER let them be alone with him. And clearly, he is unpredictable.If he were to ever hurt one of the boys or attack the Border collie again, it could be worse. And we would never forgive ourselves.

After much thought and heartbreak, we have made the decision to put him down. We just feel we have no other choice. I looked into rescue organizations, but he is not a candidate since he has attacked twice.

 But I still just feel heartbroken and guilty. Anyone out there had a similar experience?

Thanks.