Locks of Love

What are covering the walls of this viewing platform?

Locks of all shapes and sizes. This tradition is not unique to Japan; I have seen it throughout my travels. Couples typically write their names and a few wishes on a lock and then lock it someplace where the view is impressive and there is something to attach it to (typically a fence). The locks are then either left their until they are removed or until the couple breaks up and one of the two returns to break the bond.

I just have one question. How did anyone get a lock outside of the fence? If you look closely at this picture you will see that there are three locks outside of the fence. Your guess is as good as mine on this one. However this being Japan, personally I suspect ninjas.