"Clip" disappears in the editor, and "nodraw" doesn't stop the player, so what should I use for something invisible that stops the player?

Your clip brushes don't show in the editor because you need to unfilter them, just go to 'view' in the toolbar, then select 'filter' then click the 'clip' selection...you should be able to see your clip brushes in the 3D window now. And 'nodraw' isn't meant to stop your players, basically it's used to make a surface not appear in game, like on the under side of brushes used for grates or things like that usually.

"The only difference between me and a madman is that I'm not mad."

Thankoo.