If you use drilled pennies as washers, just be aware you're shortening the lifespan of your hardwarecloth (possibly of the screws too, depending what kind they are). When you put dissimilar metals together like that (copper + galv steel) you get chemical reactions that eat into the metal. I wouldn't recommend doing it where long-term strength is important (arguably including a chicken run, although everyone's situation is different)
Pat
Pat