Oh I feel your pain. My ds2 is 6 and a half and I feel like we live in a prison. Every day it seems another need to secure something arises.
Currently we have UPVC front and back doors. We keep the front door locked and the keys on our person at all times. The back door key is kept on a hook up above the frame of the back door. We keep all our windows locked and the keys are hidden at the back of a kitchen drawer for when we need to open them (usually only when he is at school or asleep).
He has recently developed the strength to open the very stiff oak doors we have upstairs, and so we had to secure up there as he tried climbing out of the toilet window up there. I just bought simple bolts from Homebase and put them right at the top of the door. We keep them bolted at all times as a matter of habit, obviously except for when we got to bed at night. As your dd is 11 and probably taller than ds, you may have to invest in new lockable handles for the doors in the house, and if your front and back doors do not have key-lockable handles you may have to sort out some sort of secuity with a key, even if it means putting a packlock on.
Family memeber have asked us what we would do in the event of a fire as we have to keep our house so secure, but in the grand scheme of things, ds escaping is a much greater risk, and his safety is paramount. We have lots of windows in the house, and have plenty of stuff in each room with which we could break a window to get out if it ever came to that.