How about life while in a metal barrel with only his head sticking out. Let him stew in his own waste while sores and abscesses do him in.
How about being realistic?
Herodotus described that as a Persian method of execution; “boats”.
After being stripped and coated with honey and milk the victim is imprisoned between two boats with only the head or sometimes the head, hands and feet protruding.
The victim is then force fed a diet of honey, milk, dates and other rich, sweet foods.
The one being executed is then left exposed in the sun to rot in their own wastes and to be fed upon by the vermin attracted by the wastes and foods.
https://en.wikipedia.org/wiki/Scaphism
That would be a good deterrent! And sat out in public
That would be great, especially if they tossed him in the Niagara River, a short way upstream from the falls.