It's always hard to know when it's time, but I won't take extreme measures to keep a pet alive - I feel that it's only helping me, not the pet - JMHO. Don't get me wrong, I've made all my elderly dogs comfortable under a vet's care. I've had to help a few dogs to the Bridge over the years, and it's never pleasant. I had an 11 year old yellow lab whose arthritis went to his spine and he couldn't get up, a 7 year old boxer with rapidly advancing cancer, and a 14.5 year old black lab who basically just wore out, developing severe canine vestibular disease that he couldn't overcome (even under a vet's care). I can't imagine life without at least one furbaby in the house!