I lived in an old farmhouse at the end of a mile long dead-end dirt road on North-central Wisconsin. I had my dogs fenced with a single run of electric fence on the inside of the fence to stop them from digging out, 6" from the chainlink and 6" up from the ground. (I timed my husky once - 6.2 seconds to dig enough to squeeze under the fence.)
The dogs food and water were in the back porch and they had a doggy door to go in and out at will. I left them for two days one fall, with enough food and water for a week - and when I came back they were so excited to show me their surprise.
Somehow - or someWHY? - an young coon climbed the 4' chainlink fence into the dog pen. The dogs treed him in the big oak in the center of the yard. The dogs took turns running up to me to say "HELLO< LOOK WHAT WE GOT!!!!" , with one of them always on guard duty at the tree!
The poor coon wouldn't leave the tree for 3 days after I removed the dogs from the yard! He must have spread the word because I never saw another coon while I lived there.
That same fence setup killed two squirrels, they both tried to climb through the fence into the dog yard - with the dogs present - and both died at the electric fence.
My guess is that the coon sufficated himself by wedging into the fence opening and compressing his ribcage which wouldn't let him take a breath.