MAJOR pet bird help!!?

I hav a pet magpie called eddie who is 1 3/4 years old and we clip his wings so he can run around the backyard. But just recently some other magpies hav been coming into my backyard and are starting to attack him. They dont hurt him but just freak the crap out of him. I hav tried throwing rocks at them and chasing them but thay are allways coming back. PLEASE HELP!!