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.

Thanks,
JW