Wow, that's a first. I have quite a few trees with just vinyl pot stakes recently moved outside. I've never had such a problem like this before and maybe I've got more suitable things for nests readily available on my farm (lots of weeds, twigs, etc.). Still, need to do something to make sure such a problem doesn't occur here!
As far as mocking birds, there is a fun way to mock them, I learned about 40 years ago. As a teenager I was getting somewhat annoyed by a noising mocking bird and I got a cassette recorded and decided to record the racket. Then, just for the heck of it, I replayed it with the player on the window sill. My brother and I had a fun time watching the original bird dive bomb the window continuously. He was very agitated by the new rival! Would be suitable material for YouTube these days, I imagine.