I have 3 dogs. All dachshund. All incredibly intelligent. My oldest one, Marty, is 12. He is slow, but is still in good health. If you are considering putting down you dog all because he's old, you don't deserve to have him.
It's sort of a rough call with dogs, they don't show you their pain too often (depending on the dog of course), my old Pitbull showed no signs of being in pain but had trouble getting up, brought him to the vet and they said his two front legs had micro-line fractures, which is like Shin-Splints times a thousand on how painful it is. It's difficult to tell, but if you know your dog, you will be able to see the pain in them.
Lehsyrus (12-03-2011)
If you're taking him to get euthanized, stay with him when it happens if you can.
Bibamus, gaudeamus.