deleting comments

As, for the second time, a certain antville user deliberatly destroyed parts of our weblog, I'm seriously looking for a solution to the following problem:

If someone who wrote a comment on a story, decides to delete this comment again later, all of the replies (added with [% this.replylink %]) will be gone as well. In our case, more than 80 replies from different people, including myself, got erased.

Is there really no way to prevent someone from deleting even the weblog owner's comments?

Thanks in advance for any help you can provide. Your free weblog service is very much appreciated. :)