why are you worried about it? potentially you could make some fancy javascript that detects if they click more than once then block them from seeing the ads, but it's more trouble than its worth.
Advise Google. They'll have more traffic information on the IP than you realise. Leave it up to them.
If you think someone is doing click fraud on your site I would advise you to contact Adsense if you aren't sure best keep your moth shut.