This is a suggestion a player on my server posted on our forums, I think its extremely clever. In short hand: It logs the first X number of block breaks of a new player. If 25% of said blocks are glass or any other configurable blocks it gives them a warning. If around 50% are the configurable block it bans them and rollsback the changes they have made. Really useful to deal with most grievers, who just join and start smashing glass instantly.