I've read on other threads here that some use this method to get rid of mice in the coop; thought this might work in the run as well: take one of those plastic storage tubs, turn upside down and cut a fat red squirrel size doorway into it. Place in the run and weight it down securely with a heavy rock so the flock can't disturb it. Underneath/inside the tub, a rat size trap baited with BOSS and peanut butter. I don't know how smart red squirrels are or how difficult they are to catch but if this one likes the BOSS, maybe it would work.