AutoCAD 2008

Tough Question - Layer Locking (Make Layer Visible But No Pick)

1.) As of now if I lock a layer, the objects cannot be moved or edited, but autocad still
highlights them when the objects on this locked layer are selected. I was wondering if anyone knows if there is a layer lock setting that would allow you to lock a layer but no be able to select it. For example I have a site plan xref in the background and I am drawing on top of it. Every time I try to work on top of this xref I end up selecting the background as well which causes the system to slow down because it is selecting the entire xref background. I want to be able to lock layer the xref is on and not be able to select it in my drawing.

Thank You