Those Miserable Squirrels!

I used to laugh at my sister who is always trapping squirrels in her yard. She releases them in the woods about three miles away. Now, I counted six this morning who were jumping into my bird feeder and stuffing their faces. I put up a make-shift shield where they jump from the tree; they knocked it down. I clipped clothes pins around the perimeter and they still get through. I even greased the pole so they've found another way. Finally, I've gathered stones to throw at them. I just have to learn to throw accurately. When they see me open the door, they scatter and shout obscenities at me in squirrel talk. Oh my! Any suggestions?