I am not a big fan of painter rings. They are notorious for splitting the decks they are mounted on. It's a real bummer to find a Morris or other old canoes with heart shaped decks that are split by "accent" hardware. For a hold-down during transport I prefer (on an open gunwale boat) to run a line between the inside and outside rails. I generally use a webbing strap and attach it close to the decks.
On my closed gunwale boats I tie to the seats.
Andre likes to drill a big hole in the deck to pass a knotted rope through, that's another option
WRT copper nails, what type of nails and for what purpose? There are multiple sources depending upon what you are looking for.
Morris attached their painter rings to the stem on the floor of the canoe to avoid what MGC describes above. This is an original painter ring, 100 years old but looking like something one could find in a hardware store today.