I have a "rat proof" pen and coop. So I do leave feed . But my feeder is in the coop, and the doors are closed at night. I do find the best is to leave the feeder in the coop, or, set it on some hardware cloth, get a metal can that fits over it, and put a rock on top at night. Or lock the treadle at night. The more food the rats can get to, the bigger the population.