I use metal lids on my barrels. That has stopped about all the chewing problems for me. If one does chew through a side, I run a bead of caulk around the hole and pop rivet some flashing over it.
55 gallon drum lid...
30 or 35 gallon drum lid...
I also set several Tom Cat rat poison blocks on top of the lids when refilling the drums with corn from time to time.
"I hunt not to kill, but in order not to have played golf!"