Thick plastic slows them down somewhat. We get bushrats up here and the smart buggers know what poison and traps are.
Keep the chook food in a metal bin andfound a mouse in there one day. Have had the dogfood in an old plastic chlorine drum for ten years, it is well chewed but not perforated so that counts as rodent proof.
When I bought my place it had massive rat holes in the skirting boards - needless to say I think the local population of rats has evolved to destroy anything in it's path. I keep my grain (brewing and surplus chook feed) in the downstairs dunny (unused and clean obviously, and sitting on the lid not in the bowl ) and with a completely sealed room - a tightly wedged door and pieces of timber blocking the gap at the base of the door the little bastards still get in. The "working" supply of chook food lives in the chook shed in a blue plastic bin with a lid that locks on and nothing has gone near it.
If I eventually get a mill I will stock up on the big blue drums for sure. They're available in lots of sizes at Capalaba produce which is just around the corner from Craftbrewer.