@Firepup650’s watched words suggestion is useful when a variety of people are posting links to a small number of spammy sites. Definitely a useful tool to have. In this case it seems like you have a user who is pushing the limits of what’s socially acceptable. You might want to consider a self-promotion policy as well. That might solve the problem without bringing in the block, which might feel heavy-handed.
An inevitable problem with blocklists is that persistent offenders find ways around it. A well-formed policy can create a community norm that channels users into more productive activity. And if not, blocking still remains a potential solution. 