Locking the focal point

I've recently upgraded my pocket camera from an LX5 to an LX15. I'm very pleased with it, other than one problem. The focal point - normally set to a small area - often moves to somewhere different, usually the corner of the screen, presumably because I have inadvertently touched the screen.
Can anyone tell me if there is a way of locking the focal point in the centre?
Can anyone tell me if there is a way of locking the focal point in the centre?