In order to catch a tricky spammer like that, one must have a full understanding of the motivation of a forum spammer. Their goal is to post links to the sites they are spamming for. They couldn't care less if anyone ever clicks on them. Successfully posted spam links on the internet are gold to the spammer, and it's how they get paid. The more links to a website all over the internet, the higher their Google page rank, and the higher their position in a Google search for whatever product they sell.
After leaving us alone for a couple months, they've been hitting us again the last week or so. We have a blocklist to block all of China, but some get through anyways. The overwhelming majority of the people who have spammed this forum, at least in the one year I've been on board, are from China. We can see their IP address, with a WHOIS lookup tool, in the Administration Control Panel.