Hiding parts of an object?

Hi there,

I’ve got a bit of a problem I’m trying to get to grips with, basically I’ve got a flat platform as a floor for my map, that has a cylindrical wall, so looks like the attached.

Outside of this is a pretty nice outdoors environment as a backdrop.

My problem is that as the player gets to the end of the wall they can look over and see the edges of the floor for the map, is there anyway of hiding the edges of the floor that are outside of circular wall?

Could I for instance park an invisible mesh over it?

I’d appreciate your help.