Definitely tailing loops. However, the problem with them is that they are caused by more than just failing to let the line go all the way back... more often than not it has to do with the how your rod is moving, how abruptly you stop it, and whether you let your rod tip drift after you come to a complete stop. In essence, your rod should start slowly and then accelerate to a crisp stop. Even little things, like how you hold your rod, and whether you just unconsciously turn your hand grip will affect where the line goes in front and behind you. My advice is to pick up a DVD on fly casting... I've had issues with "wind knots" in the past, and having it demonstrated is the only way you'll be able to get past it!