What's the best way of securing patio doors?

The patio doors just have the standard lock and key in the middle of the door. What's the best way to make the door more secure - locks top and bottom, if so, what kind.

Or is there some other device that can be used to block the runners and stop the door from being opened?

Thanks

Take a look at the options available here. You should be able to pick these up at any locksmiths and most DIY/hardware shops.
Leo

Hi Leo - Thanks for the info.