When is it time to put a dog down?

Question
My 16 year old Basset Hound, Katy was possibly diagnosed with cancer several years ago. There are lumps in a few places on her body. She does not appear to be in pain and she still has a very healthy appetite and does all the things that a Basset does mainly barking and snooping. She walks with a limp that does not appear to cause her pain but she is 16 yrs old. What would you suggest as to when to put her down? Thanks

Answer
This is a difficult decision, one I have tried not to have to face.  I will anyhow.  I think the real factors are is the dog in pain, and does it still enjoy life.  It sounds like your dog is still living a good life, so I see no reason to give her up now.  If she starts showing signs of pain or just loses interest in life, then it will be time.