If you are making a guide or something like that, I think the only way to keep people from disrupting the flow of it is to reserve the posts following the original one. You can also request for a mod/admin to lock your thread, but I'm pretty sure that prevents you from posting on it in the future as well. May I ask why you wouldn't want anyone to post on your thread in the forum?
Oh ok. To my knowledge there is no way of doing this. I could be wrong, but I think you might be out of luck on this one.
You can ignore the user. What you can do is first, click on the users post, then hit the "Ignore" button
