There are a couple of things you can do. One is an aluminum plate, but most of the time that's hard to do. The other is to use 3M 1181 copper tape. If you shop around, you can buy a 1 inch wide roll about 50 feet long for about $20. You have to be careful because the edge is SHARP! It curls easily too, but with a little care, it makes a passible ground plane.