.htaccess on multisite with childthemes – how to: deny, allow

Hi there. I want to use a multisite WordPress install with child themes. I want some themes to be public and others to be only visible for some IP numbers.

The multisites work fine. I do have some sites and I am using the child themes which depend heavily on the parent but are in some areas different. Works like a charm.

But now i need a “rewrite voodoo” who can help me out with the .htaccess.

EG. I like to have this site to be accessible for everyone: website_1
But this site I do not want to be accessible, only for one IP address: website_2

Can someone point in the right direction or share some ideas or even give examples to what i should think of?

I was thinking of having a .htaccess in each child theme, but that did not succeed.

Thanks in advance,
Prox