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