Implement a way to shut a server down momentarily

I am an admin in a server that gets targeted for raids semi-frequently, and there really isn't much for us to do about it. My idea for a feature that would help us out (and i'm sure other people would find it useful too) is a way for us to lock the server for a little bit to make it so people can't join without deleting invites or anything. This would be incredibly helpful, especially since all the anti-raid bots and stuff haven't really worked for us.