Even though I've had dogs for about 20 years, I'm still a little inexperienced about many things because I've really just had the same dogs for a very long time.
At one point I had three. The two girls started fighting viciously (blood, going for the throat, the whole 9) so I had to re-home the youngest. The oldest (14) was put to sleep 3-4 years ago. Her mind started to go and one day when I came home from work she was down in the yard and wouldn't get up. That was a fairly easy decision to make.
That left little Hughbert all by himself. At 17, my doxie is not doing great and I don't know what to do. He doesn't have any terminal diseases, and aside from some meds for separation anxiety (started after all the other dogs were gone) he isn't being treated for anything. He isn't blind, his hearing might be OK but I think he just doesn't bother to listen any more. His house breaking has gone completely by the wayside, and just goes where ever and when ever he wants, showing no disregard for it. He'll sit in a puddle of his own pee, wet the bed at night and stay there, poop on the floor and walk through it, smearing it all over the place. Most of the time I have to put him in front of his food to get him to eat. By this point he has about 8 teeth left. He will walk into corners or tight spaces and start whimpering because he is "stuck." He will also hang out in dark hallways.
Because of his age he will get ear infections or UTIs, and the Vet always gives me the "well at his age..." preface before they discuss treatment. My wife and kids tell me that their friends feel bad for him when they see him, although they have never said anything to me. I am starting to wonder if I shouldn't let him go. He is past the upper range of his breed's life expectancy, but the oldest on record was 24. He could potentially go on like this for a few more years.
He isn't happy; I know that. I can't remember when the last time his tail wasn't between his legs was. But that doesn't mean he wants to die either. He can't tell me if he would prefer living a slowly decaying life or end it with some dignity. That's kind of a heavy philosophical question for an animal is the basic intellect of a 7 year old.
How do you know when it is time to put down a dog that is still technically functioning, but only in the most rudimentary way?