Am sure you know they have the domain whois protected, but.. i would call these guys, and tell them that one of their clients is fraudulently copying your website, and you want LiquidNet to tell the owners of casinobonusplanet.com to stop, and remove, otherwise you will take legal action. A few affiliates have done this already.
Seriously man, you got a great site, with great traffic, don't let anyone destroy it.
LiquidNet US LLC (Whois Protection Dept.)
Whois Agent (fd676usv@whois-shield.com)
+1.5108700646
Fax: +1.5108686446
1040 SE 7th Court, Apt 307
C/O bonuscasinoplanet.com
Dania Beach, FL 33004
US