There was another thread on this made a while ago...it actually makes you invincible if you do it correctly.
You make 2 paths: 1 long, 1 short. The enemies will always take the short path, so they will go down that one. Then, put a peon tower at the end to block it off. They will go all the way back up the route, to go down the long path, as it would be the only path. Then, you can clear the peon tower at the end of the short before the enemies reach 1/2 of the long path to make them go up the short path now, because it would supposedly take them there in a shorter time. If they don't turn, put a peon tower at the end of the long path. Repeat ad infinitum.
Not my tactic, from another topic.
