Personally try to avoid physical confrontation - as Dan hinted you have no idea what you are getting yourself into, sure smash it up, then find the following day your driveway smashed up/vandalised etc, you repair it and its done again and again and you get into a stressful situation. Even worse case scenario is you go out to your drive a few days later and twenty bikers rock up wanting 'a word' just how tough can you be then?
Put up additional signage, you never know that might just sort it. If not, leave a note on the bike reminding them that its a private driveway and its important you have access to it at all times etc. Dialogue should always be the first effort so you know the full facts of whats going on