From my experience, the only thing that keeps them out is a cage made out of 1/2" fence wired completely around the feeder with a door wired to the bottom and secured to the bottom of the barrel with metal clips. They can hang on it all they want but they can't get to the corn after months of trying.

I had squirrels chew holes right through my feeder lid and bottom corner of the barrel after placing a cage on my feeder back here in pa. Now I use only metal drums and lids, let the little B@$+@rds try it now. They wasted 100 pounds of corn last time by chewing through the lid letting the rain run inside and rotting the corn. I am ready to open the season early on them. Think I might get one of those GAMO whispers for when I am in the stand archery hunting. I used to take old arrows and broadheads but it looks like a pungy stick field by the time the deer show up right before dark. the pellets would be a lot cheaper and it would kill coon as well.