Good idea trendie but that wouldn't have nabbed Jester since he was kind enough to post a little differently each time. It could also result in, say, an urgent question that a member has posted on two or three fora being deleted. I'd like to prevent anyone with fewer than ten posts from posting a URL, and that is codeable, but, once again, it could prevent an honest n00b from posting an innocent URL.
Any automatic system is likely to have its flaws, which is why we're here - if, in my case at least, admittedly a little slow to act on occasion.
Regarding the flagging idea, well, you members do an excellent job of that already. No spam seems to go unnoticed for more than a few hours and you're always kind enough to alert us to it, for which thanks.