For me, it's just a feeling I get when it's the right moment. I'll see my dog's health declining, and I'll know the time is coming, and maybe his or her life just seems to be getting worse and worse. One day I just know today's the day and that's when we go in and have it done. My first time, it was after a neighbor complained about the smell coming from my apartment. My dog was incontinent, and even though I cleaned up every mess as soon as it happened, it still smelled. Another time, I made the decision with my head instead of my heart, when my dog lost his fecal control. I still don't feel right about that decision, even though the vet said it was the right decision that day. (You may be different from me, though. You may make the decision with your head and feel good about it.) Last year, I had a dog come down with weakness, swollen legs, an intestinal bleed (bloody poop) and the vets did everything they could for him, but he was so sick and clearly suffering, that I couldn't make him go through that and we went together to the vet's office. I sat on the floor with him and gave him his favorite neck stretches while the vet did his job. It was horrible that he went, but it was a good way to go. It's hard to make that final decision, when the dog is going through the normal decline of old age, but you'll know in your heart when it's the right moment. As the other person who answered you said, you can talk to your dog and tell him it's okay if he goes. You can even talk to your dog and ask him if he wants to go. You may be surprised when you get an answer, but he may look at you a certain way, or just behave differently somehow, that will tell you yes, he's ready.
