My suggestion is for cyclists mainly but it could work for walkers if they wear a brimmed hat which I do when bushwalking. Apparently walkers are less likely to be attacked as we cyclists are being advised to walk our bikes through the danger area.
Mitre 10, Homehardware and Bunnings, to name a few, sell safety glasses (made as sun glasses as well) - for Tradies. They are even tax deductable for those working. My friends and I wear these for cycling and bushwalking.
Recently I came off my bike and went flat forward on to the concrete. My helmet was slightly scraped on the left but the left lense of my safety glasses is so scratched from the concrete skid that they are unuseable. Proof that they work as I was saved from a very bad graze wound on my upper left face by the glasses.
I concentrate on my riding and do not worry about the Magpie. I have been hit numerous times by Magpies, in the area between Thirroul and Kiama, but they have never drawn blood. I heard of one rider who had the Magpie grab his ear and hang on - that hurts but is not dangerous.