There is only one true way to protect whatever it is you are trying to protect and even then someone always thinks of a way around it ..
Basically encrypt your html/php with a proper encrypt program like ioncube or zend, then get yourself a php programmer to build you a script that will encrypt and decrypt the page(s) as an admin function, this script should also allow the ability for the encryption to change each time the page is loaded or in this case each time it is viewed.. this is possible but I wont say its 100% foolproof..
There is only one true way to protect whatever it is you are trying to protect...
Yeah, it's called not putting it on the Internet. If you put it online, someone can take it from you for free. The level of difficulty in doing so will vary, but you can't stop it. If you don't want other people to have it, don't put it online.
Well again there are things you can do and yes you can make it hard as heck for some people but yeah nothing is 100% foolproof.
Having the attitude "well if you dont want someone to have it then dont put it online" dont help anyone, the original poster asked a question so instead of shooting down any hope why not offer suggestions ...
Here I will expand on my post and again I am not saying this is perfect or this is the solution to everybody's problem about protection.. This does not use ioncube nor zend and I am sure some programmers could hack away at it .. but some protection is better than none..