Squirrels and birds are frequent victims of open chimney flues. This will prevent squirrels and raccoons from breaking inside. Be sure to anchor the screen with wood screws and washers. Painting the screen will make it less noticeable. Keep your home in good repair.
Animals are opportunistic.
If they see a hole, they will use it. Repair damaged wood and broken soffits. Don t make it easy for a squirrel to chew into your home. Don t allow tree branches to overhang your roof. Animals will use a tree limb or climb a tall shrub to access your home.