With the premiere of Season 4 of The Walking Dead drawing closer, AMC continues to release new teaser trailers. The latest tease carries a very simple message: Nowhere is safe. In the video, Carol tells a young girl, "If you want to live, you have to become strong." Then, Glenn barks out, "There's walkers in D." It seems walkers have somehow made it inside the prison. Hershel warns, "Everything we've been working so hard to keep out, just found its way in." The Walking Dead Season 4 premieres on Sunday, October 13 at 9 PM ET on AMC.