You will always have a few "punks" that bark furiously,but refuse to come any closer.
The funniest thing I ever saw involving a squirrel,was during a blackpowder hunt a few years ago.I was up a tree and two squirrels got into it below me tree.After the fight,the loser hopped away,letting out a little grunt every time he hopped.He would look back at the other squirrel and curse.True story.
I use my mouth to call them.