If you plugged this in, wouldn’t the breaker trip?
Not unless the resistance to ground through the fence is low enough to result in a high enough current, and that's very unlikely (unless the breaker was a GFI type).
If someone touched the fence (let’s say in bare feet), don’t you think the human would have a higher resistance than the fence’s connection to ground, and not get shocked?
Both the resistance of the fence to ground and the resistance of the person to ground will both be much higher than the source impedance of supply.
Even if the resistance to ground on the fence was low enough to result in several amps of fault current, the fence would still be at 120V to ground, so the person would still be shocked.
