Alicia, I kind of know how you feel. For the last few months I've been contemplating this decision, but I realize now it's definitely not Sassy's time yet. We have here on some new medication that works great. She is a little stiff after she lays down for awhile but not limping/crying in pain anymore. It helps alot. Having to watch your dog age is not a fun experience. I believe that only you will know when it's time. When they don't get up to eat, enjoy things they once used to, cry in pain every time they walk, and are just plain sad, then you will know. I am sorry you are going through this with Thunder. I know it's hard, and whatever decision you will make I know it will be for his best interest.