I use a aluminum trash can with a thick outdoor trash bag lining it. Then I set my entire 55# sack into the can+liner, tie the bag loosely, put the lid on, then put a concrete brick on top of the lid.
Got the Al trash can from my local Menards (Home Depot without the incessant orange color) for under 20 bucks.
I thought about plastic, but we have mice, and they'll eventually chew it, I"m sure. They chew everything else.