They used to sell a chain of some kind to put in the bottom of draperies to hold them down. You might try the drapery department of a fabric store if you happen to be in one sometime. Also beaded chain comes in different weights at the hardward stores; maybe that might work?
Just chiming since the subject of what chickens will eat and the word "nickels" was touched on.
One Sunday morning when I was about 5 years old my church offering of 25 cents, composed of 2 dimes and a nickel, was grasped in my sweaty little hand. We stopped somewhere for something and somehow I ended up filling that hand with grain to feed to some chickens - my change was underneath the feed. ...You see where this story is going... When the chickens had finished the grain, my two dimes and nickel had disappeared as well. I cried, devastated because the chickens had eaten my offering. I'm over it now, though.
It's amazing the large and weirdly shaped items that can disappear down a chicken gullet!
How about using pencil led? Not the writing kind lol, but the stuff that you use for fishing. I think it would be heavy enough and it comes in rolled up lengths that you can cut to length.
Well, Lilith ate piece of broken glass the size of my thumbnail once. She's also eaten at least two soda can tabs that I know of, before I broke DH of the habit of pulling them off and tossing them in the yard.
This chicken LOOKS for non-edible things to eat.
Gonna keep experimenting.