PrevenChew Stainless Steel Mesh is a great rodent excluder.
Copper Mesh for Pest Control Mouse, Rat, Slug, Snail, Insect and Rodent Control Rodent Mesh, Snail Repellent, Pigeon Deterrent Pest Exclusion Wire Mesh Roll (3M) - Walmart.com
Wire Mesh Screens for Pest & Rodent Control - TWP Inc.