| Hadrians Wall
No good for keeping the Jocks out.
Big wall that the Romans under Emperor Hadrian built. Stretches from roughly Newcastle to Carlisle. In Roman times this was to prevent hordes of wild Caledonians streaming south to rape and pillage.
In modern times the wall is useless, which means that lots of sweaty socks come south and take up jobs in the British Government.
Conversely, with a little work and a few stewards, could be used to keep the english out of Gods Green Land.