some stories on this board scared me.... so many peoples saying they got banned because someone clicked their ads many times... How is it possible to prevent this? Is there some script that could prevent multi-click, or just turn off the ads after they have been clicked?
There is no way you can prevent others from multiple clicking your adsense ads or sabotaging your site. But you can track the adsense clicks by using some tools available free of cost and reporting back the fact to google if there is any suspicious activity.