Ningasquirrel makes a valid point, several points. And I forget that a thread is about the OP and tend to offer general advice or points to ponder. If the critters have stored food they are going to be tougher to evict.
And the coons searching for a weak point shows the need to consider what is the consequences of closing one problem. Kind of like putting one of those long and strong door jamb plates on an entry door so can't be kicked in might mean getting your windows smashed in instead. Fixing the door jamb after a break in might have been cheaper.
Still, we have to circle back and admit that prevention will always be less costly and less complicated than the cheapest solution to a problem. In this case, protecting the feed might well require poisoning to solve the problem. But others might learn from the OP's quandry and solve this problem before it every shows up in their coop.

