well, the one reason you can't always load a fence up is that it would
typically be grounded.
I have heard of people using metal fences to act as HF antennas, but they
had to be totally isolated from the ground.
Case in point, many farmers who have miles of 3 strand barbed wire fencing
on wooden posts will use the top strand as a beverage antenna or low band
receiving antenna.
I think 4 miles of wire would make a pretty good receiving antenna.
Most chain link fences use metal posts in the ground, and the chain link
itself is typically treated with a plastic protective substance, or painted,
which can lead to problems with continuity.
As a ground system though, it would work pretty good under a vertical even
with bad continuity between links.  Just having all that metal under a
vertical would improve reflections.
73
Colin, V A6BKX