Like/Dislike system without authentication

Like/Dislike system without authentication

I developped a Like/Dislike system on my website WDMND.com.
I am using asp.net with C#.
My goal is to get the feeling of every visitor, even without authentication.
So, I limited the vote on every single control to 1 per IP.
I realised that two users of the same family can't share both their
opinion, because they have the same IP :(
I tought myself "No problem! I'll just limit the votes with the MAC
address :D". Unfortunatly it is not possible :P
I then had the idea of using cookies! The thing is... Some trolls will go
like :
while (!timeToGoToBed)
{
vote --;
cookie.delete();
}
This is where I am in my reflection.. I don't really know what to do with
it. Should I just keep it like this or is there a better way to do this?
I need your opinions and suggestions!
Thank you very much!