Here's a video of my solution to this one.
http://youtu.be/clYaian7rY0

If you put your two barricades in the positions shown (near the front) and then just keep spamming skeletons at the front and replacing the barricades as needed, it's simple. When a ranger shows up, place a skeleton right behind him or to the side, so that when he fires he doesn't take out a barricade or kill a lot of your skeletons.

---

Tcarr9's Tiny Heroes video walkthroughs are available on YouTube: http://www.youtube.com/user/Lordkalvanmidnight