Max Items allowed in a Slot?

I currently have a slot that holds a certain content type for secondary URLs in the system. Our business rules state that we should have at a max, 3 of these content types in the slot. The content type for the secondary URL itself, should only point to 1 other page in the system.

Is there a way to restrict the number of things allowed to be placed into a slot? I have max results in the slot turned on to the specified numbers, but it looks like it just returns that number instead of restricting the user from linking the objects.