re: When to know when making right decision of having dog put down?

If he stopped eating and seems miserable it is time to put him down. Cruel to him if you don't.

Recently had to put an old girl down. Devastating and I'm tearing up as I type, but I didnt want her to suffer anymore.

Say your goodbyes and know he was always your friend. Be a good one to him. A "natural death" is painful and torturous. Before the vet will euthanize him, they will give him a sedative and allow you some time alone while he's not feeling pain. Then,when it does happen, he will simply go to sleep with no pain, the memory of your loving presence his last.