Web works for this too. This is because the AI is poorly written and doesn't know how to cope. The challenge rating from D&D assumes the creature in question is not so far beyond stupid as to try to get out of a web when it's being shot at. Livonya's mod, which is part of the co8 mod, I believe corrects this problem, improving the AI, and making this sort of abuse impossible. At least, that's what she says.
