Chicken. Wire or hardware cloth put over the end n held in place with wire , rope, clsmp whatever you choose , something shaped like this or this
You wanna keep a good flow rate , so to small is a consideration, but you can easily buy or make your own going off these for ideas , the second one you could bolt on rather than.tie.
These pics should get ya started on the general idea of what your wanting , the specs n all that you can tailor to your taste
