I agree with everyone, I would use hardware cloth for sure. I haven't yet found anything better. 

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You've been lucky. Mice, rats, fisher cats, weasels, snakes can all get through including juvenile raccoons. Great for larger livestock but chickens need more protection. EVERYONE loves the taste of chicken AND eggs.This is the wire I use not easy to cut and haventView attachment 1808918 lose a bird with it yet![]()
Srry I never put int he factor of the small ani.als as we dont have all of them for the mice and rates we have a pair of cats which breed and we just kept the strongest kitten and castrated them after we had enough so there is no wild cats cause they chased them away and they eat rats and mice aswell as any birds they getYou've been lucky. Mice, rats, fisher cats, weasels, snakes can all get through including juvenile raccoons. Great for larger livestock but chickens need more protection. EVERYONE loves the taste of chicken AND eggs.
How tall is your picket fence?
Will you have something covering the top?
Height almost makes what to close 4" gaps with moot...about four feet high