I have searched all around the web for .htaccess tutorials, and there are a lot of them but none seems to offer a solution to this particular problem: I have rented webhosting space and I am running two domains off of one account. The two sites are totally unrelated and I don't want to be able to access the files of one with the domain name of the other. Here's what I mean:

Assume I am running two sites, biology.com and physics.com (just an example), off of my account. The directory structure is like this:

index.php // this file takes all requests and sorts them out by domain name

/biology
/biology/biology-index.php
/biology/biology-page1.php
/biology/biology-page2.php

/physics
/physics/physics-index.php
/physics/physics-page1.php
/physics/physics-page2.php

So the two sites are separated, and when you type in biology.com you get redirected to biology.com/biology/biology-index.php, and when you type in physics.com, you get redirected to physics.com/physics/physics-index.php. That redirection is done with the index.php script and it works like a charm.

BUT, someone could type in biology.com/physics/ and get the physics-index.php page while having the biology.com showing in their browser address. And I have noticed that it doesn't just take someone typing it in like that for it to happen--it has happened as a result of search engine robots that mangle the address, etc.

So is there any way to set up a rewrite condition and rule to prevent any request with a host of biology.com from allowing access to the physics pages, and any request with a host of physics.com from allowing access to the biology pages?

To whomever can solve this, thank you so much, in advance!