Yeah, don't forget to lock the barn after the horse gets out.
Looking at the logs to see what they do after they break in after watching them try forever is a great idea. If they can break in they can cover their tracks and only let you see what they want to let you see and may have done other things to aide them and you would never know it.
If you notice someone persistent in getting in it is best to block them and not wait till after they got in as if they were persistent then they are not just out to check out your server they are looking to do things to it you wouldn't like.
Good luck with that. I will be looking forward to getting spam from your server on behalf of those whom broke in some day.
