I read something on the meat rabbit list about pennies in a ziplock bag with water to repel flies. It seems that if you put a few pennies in the bag, fill with water, and hang it, the flies will leave. It has something to do with the fly's optical ability? I went and looked it up and haven't seen one person that says it doesn't work. I will be trying this tomorrow in the rabbitry! So, total cost...4 pennies and a ziplock bag. Can't hurt to try!