I am SO SO lucky in that I have always had dogs and cats together and have never had a problem. They love each other, sleep together and clean each other. There always have been both cats and dogs in this house, and the yard. Whenever a new one comes into the house it's already been established that both cats and dogs live in harmony here and the "newbie" just better fit in. They always do. Not so with others I know, my daughters two dogs killed her new kitten while alone. I'm so sorry for your loss but please don't put your older dog down and resent your new pup. Ever vigilent, ever aware and training NOW, while still young.