How prevent gui button from activating navmesh?

I put together a nice point and click locomation system as per the mecanim examples navmesh scene. Everything works fine, but I also have a series of gui tool bars and menus with buttons that, when they are over the navmesh area, also activate the navmesh, when clicked, moving player's avatar to that location. I've tried putting the gui and navmesh in different layers but to no effect. Anyone know how to stop gui buttons from activating navmesh? Thanks!