Site visible just for clients (no public) without loggin in

Hi.
I`ve created the website http://www.poliklinikack.cz, using Maintenance Mode.
Now everything is ready and I need to show site to clients without need to log in.
Setting every single I.P. adress is not possible too.

Is there any way how to setup link where all page would be visible without any logging in or passwords? I mean only people who have that link can see it and it won`t be the http://www.poliklinikack.cz.

Thank you for help!