If they did it frequently enough to create a detectable pattern, the votes would start to be ignored to varying degrees. As you point out (though this wasn't y

If they did it frequently enough to create a detectable pattern, the votes would start to be ignored to varying degrees. As you point out (though this wasn't your theme), the ranking algorithm on the front page also helps mitigate the problem. Stuff upvoted by a ring will sink back down if it doesn't catch on with other users.