I had to put down my father's dog, a husky/shephard mix, 10 years after dad died. My mom had kept the dog and in his old age he started losing control of his hind quarters, needed assistance to get around, lost control of his bowels ... and mom asked me to put him down.
He still took great joy in cleaning out the cat's food dish. I picked him up and put him in a wheel barrow, wheeled him from mom's house over to my dad's shop and put him inside. His last "ride". I put a big lump of wet catfood in a dish in front of him, he automatically started licking the dish clean with great enthusiasm. I pet his head for the last time as I moved around behind him while he devoured the cat food. I pulled out my dad's .22 pistol and pop-pop to the back of his head just as he was finishing. He never felt a thing. I dug a hole in the corner of the back yard and buried him beside other family pets long passed.
That was emotionally the hardest thing I've ever had to do in my life, to put my dad's dog down. My dad had to do the same when he was younger, only after doing it myself did I fully understood the emotional stress involved. I never want to have to do that again. It is so much easier to let the vet do it painlessly with a couple of shots. I was later told in the old days one would ask a close friend to put down the family pet and vice versa.