I rely on a healthy mockingbird population. One Saturday, I looked out the window, and saw a mockingbird giving a 6 ft black rat snake a hard time. I went out to see where it was going. As I watched it go under my pickup, I watched another equally long snake meet it, and they coiled together. As I was thinking of the 22 babies that would come, in the corner of my eye I see a mockingbird attaching a 5 footer coming from under my shed. I made an immediate decision all 3 are done. As much as I see the black rat snake as essential, living next to an old orchard field, they are so very plentiful and overpopulated. 4 years later, I find a black rat snake once in a while, and leave them alone... Unless they find a nesting box.
That said. Hardware cloth is your friend.