I think you're missing the point. These SEO hackers don't announce themselves by defacing your front page or deleting your database. They insert hidden links in your HTML to boost their PageRank and it's in their interests to go undetected for as long as possible.
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[ 6.4 ms ] story [ 325 ms ] threadI'd set up a cron job to check the database once a day or 12 hours or so. That's more pre-emptive.
So basically theres the possibility that you'll be crawled before your daily cron runs...