Palisades look distinctive than your bog-standard fence, using whole logs with sharpened ends as fortification.
Posted under Tags
I had the same idea of a tag for iron fences once, but then I realized it was basically just fence + ironwork. Not sure if there's much need for a tag like this unless you intend to use it as an umbrella for things like random barricades and chain-link fences and whatnot.
I can't help but notice that someone's using this tag for metal balcony railings (post #5360668) as well.
Speaking of balcony railings, I think it'd be helpful for someone to write a wiki for it, so it'd be less confusing if the surrounding cover should be tagged as fence / iron_fence or a railing. The official term is balustrade, but the tag not existing tells enough.