Along the bottom of my run (it is a carport that is 12'x21') we will have 2' of sheet metal all the way around, plus 12" will be buried in the ground to prevent critters from digging under.
The rest will have 1" welded wire and be fully enclosed. I will shut the chickens up at night for a while until I'm certain nothing can get in and by the hottest part of summer I'm hopeful I can give the chickens their choice of where to roost. I'll add some roosting areas in the run right down the middle so nothing can reach through and grab them.