Random rotation

Hi forum

Im using the code from this tutorial

http://www.kirupa.com/developer/acti…dom_motion.htm

and im trying to use it for a butterfly, ive got it moving ranomly on the page and I have got it rotating in one direction using the code below . I want it to change the direction that it rotates in a kind of random way

here is the site

http://www.wedding-makeovers.co.uk

onClipEvent(enterFrame) {
this._rotation -=6;

}

if there is any one who can help that would be great