$.fn.setScrollAD = function(){
    var obj = $(this);
    obj.show();
    var cssTop = obj.css('top');
    $(window).scroll(function(){
        var bodyHeight = document.body.scrollHeight;
        var scrollheight = document.documentElement.scrollTop;
        var objTop = parseInt(scrollheight) + parseInt(cssTop);
        if((objTop + obj.height()) < bodyHeight){
            obj.css('top',objTop);
        };
    });
}