Parts of your question are quite confusing.
1. When you say you want to know when they use your article - does that mean read it? Or does use have some other eaning
2. You said you don't want it checked out, so do you mean you don't want them to be able to save it locally?
Its too confusing, anyway something like this ?
http://www.mendeley.com/..
Edit 2:
Oh you want a content leasing system. So basically they are leasing your article from your site. Oh the logistics behind that are horrible. So you basically want a system where people can lease your article and you want to know where those articles are basically used. Yet allow all users to still be able to see it in other places.
The issue I see will crop up, I don't think anyone would take the full article, Its more of an all or none game. If they take the article they would rather have exclusivity over it, not share it. I understand you just want to track your working among sites, that's quite fine.
Im running the quandry in my head, but as far as I know, there is no article leasing / tracking system which was ever succesful. Sorry