Make it clear to potential members that my forum is "Still Under Construction?"

Have a bit of a problem. Although I've kept my forum under wraps until now, somehow people have found out about it and a trickle has already started to join     

Well I don't want anyone to join until I've properly stress-tested it and completed everything. So is there a way to a) Block people from joining until I've completed it or b) Make it clear the forum is view-only and "Still Under Construction?"
Thanks

There is maintenance mode
Under Admin -> Forum Settings

That stops non admins from logging in/viewing

Okay cheers will check it out.


Can you set it indefinitely or is there a time period after which you get penalized for it?


With the latter I'll have to dip in and out of maintenance mode until the forum is properly finalized, so asking in just in case.


Many thanks

It is either on or off no time control.