You could get what is called shade cloth. Nurseries use it for protection of delicate plants from summer sun. I would guess a local nursery would have it. Tarps rot due to ultraviolet. I expect that shade cloth and bird netting does too. Also, you could try stringing polypropylene twine all about overhead. Hawks and owls do not like it , but it must be pretty closely strung to work. It is fairly durable and very cheap.