Or alternately you can respect the landowner (yes I know its really us) and only use the keys that are issued, on trust, for the duration of an event. Relations with the FC can be delicate, and abuses of their trust could be a great way to get the whole sport embargoed.
I now have three keys. One that used to work nationwide although I suspect it would be little use now. One that was supposedly a 'high security' lock which I have found on parts of Cannock Chase. A new padlock with a completely different design of key - rather like a small Yale but which appears to be on all the main Cannock gates.
All courtesy of the FC through good working relations over the years.
Going slightly off-topic - does anyone know whether the agreement that British Orienteering have with the FC has been adapted/renegotiated for the new event levels? I remember seeing a document that showed the amount paid for access depended on where the event sat on the old 5-level structure...