Chickens will eat ANYthing. Epecially if it's shiny -- I would try to use a rake and see if you can't get most of that picked up-- at least in the area where they will be. Sounds like a lot of work. We have a HUGE party every year at my house for the 4th of July. People come here and shoot off their fireworks and we even have a DJ that plays music. We have a TON of trash left over from all the spent rockets, fireworks, etc... I spend a week with the kids every morning and most evenings and we walk the yard with trash sacks. We pick up anything we see, no matter how small. We've kept our yard pretty darn clean even after years of hosting these events! I will ocassonaly find something I missed from the year prior- but when I do my first mowing out in the back I take another trash sack with me so I can stop frequently and get anything I've missed. I have about 3 acres to search, and we manage well. Just anytime you walk out, take a Walmart sack with you and pick up anything you see. It's a real PITA for sure. I understand.