I've added a second paragraph to the Terms new users must agree to when registering here. It states, in bold:
If you are a human or a bot and your sole purpose is to create posts to link to external sites (including hidden links or links placed on your user profile) your account will be instantly terminated and your IP will be banned for life. By registering you assert that you are not a spamming jackaloon.
Doubt this will deter a single person/bot but it felt necessary to make this more obvious since I delete accounts each week.