This works for me 
As suggested put the css styles in
body, div
{
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: -moz-none;
    -ms-user-select: none;
    -o-user-select: none;
    user-select: none;
}
also add these to allow selection within form fields
input, textarea, .userselecton
{
    -webkit-touch-callout: text;
    -webkit-user-select: text;
    -khtml-user-select: text;
    -moz-user-select: text;
    -ms-user-select: text;
    -o-user-select: text;
    user-select: text;
}
Note the -moz-none thats needed or the reenable for inputs doesnt work.
for IE I add
<script type="text/javascript">
    window.addEvent( "domready", function()
    {
        document.addEvent( "selectstart", function(e)
        {
            if ( (e.target.tagName == "INPUT") ||
             (e.target.tagName == "TEXTAREA") ||
                 (e.target.hasClass("userselecton")))
            {
                return true;
            }
            return false;
        } );
    } );
</script>
This not only prevents selection of background text but allows selection on inputfields and and element you put the userseleton class on.