How to check copper to copper clearance?

I use OrCAD PCB Designer Professional 17.2.

My PCB partners require 6 mil clearance between copper objects.

The board has 4 layers. I use a through via array to connect a plane on layer 3 and other on layer 4. To ensure 6 mil clearance, I must add plane on layer 1 and 2.

If I omit layer 1, I want the layout to notice me the error.

Question is How to set up constraint to solve the above problem?

Please refer the below picture.

Layer 4

Layer 3

Layer 2

Layer 1

Thanks,

Tom