"whois" is a standard command, it's not just from that website that you can access that information, you can get it from many other websites, and some operating systems.

Proxy registrations are available in some places, I don't use them, I'm not even sure if it's allowed...

If you are concerned about people looking you up, just put down an address you don't care about/don't live it.

P.O. boxes are not allowed.