As far as I'm aware (and please do correct me if I'm wrong), Leeds have never had their ground sold out from under their feet by their own board, been 28 minutes away from relegation from the FL and probable extinction, had to spend two seasons playing "home" games 70 miles from Leeds and then...
When we lost (well, the replay anyway).
If we're intent on commemorating something, losing a Cup Final and getting relegated probably wouldn't be what I'd go for.