Chickens like to scratch and forage, so food being hidden isn't necessarily a bad thing, unless it gets wet and moldy. I rake the run almost every day to prevent any mold problems.
I have 12 Buff Orpingtons and they tend towards gluttony, but a 50lb bag lasts 2-3 weeks. They have a large run and we planted a small raised bed the length of on wall of the run, to encourage more bugs, so they are doing a lot of foraging.
Our neighbor has been visited by rats and a skunk...