What is the best-feed hopper design?

There are many very effective designs of feed hoppers available both commercially made and constructed at home. The keys to a good design are that the hopper protects the food from the weather; as far as possible it prevents food from being spilled onto ground; and that scavengers are unable to rob it easily. One home-made design that has stood the test of time is made from an ordinary 25 litre metal drum with slots cut in the baseain copy :

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