Disable right click without any message, just silent action. Visitor cannot see page source by right click (but still can open it by CTRL U, or just copy CTRL C).

Simply paste code below under body tag.

<script language=JavaScript>
<!--

//Disable right click script III- By Renigade (renigade@mediaone.net)
//For full source code, visit http://www.dynamicdrive.com

var message="";
///////////////////////////////////
function clickIE() {if (document.all) {(message);return false;}}
function clickNS(e) {if 
(document.layers||(document.getElementById&&!document.all)) {
if (e.which==2||e.which==3) {(message);return false;}}}
if (document.layers) 
{document.captureEvents(Event.MOUSEDOWN);document.onmousedown=clickNS;}
else{document.onmouseup=clickNS;document.oncontextmenu=clickIE;}

document.oncontextmenu=new Function("return false")
// --> 
</script>

source: DynamicHTML