Trying to be a good kid: Citation for students

I'm sitting in a Panera at a mall, since this is the only way to get both breakfast and wifi out here in the sticks.  I was getting nervous about all the repairs that my car needed, and decided to bite the bullet and take it to a VW dealership so I could get people who know their business to fix it all.  They're probably going to be working on the car through lunchtime, so they gave me a ride to the mall so that I had a slightly nicer place to twiddle my thumbs.  I am smart, though, and instead of thumb-twiddling, I have work on hand, so I went for the wifi and coffee.  I fear that the repair bill will be frighteningly close to $1000 $1300 (fuckfuckfuck), but I couldn't see any way around it.  This is why the devil invented credit cards, right?

Speaking of work, one of the syllabus-related matters on my mind is how to explain thoroughly to students how to avoid plagiarism.  I constantly sit on the fence in the argument about whether these kids nowadays don't properly understand what plagiarism is or whether they're just lying little sacks of shit trying to get away with whatever they can.  In any case, one must assume the former before getting to know them, so I need to walk them through the whole deal. 

What all should I be covering?  Obviously, there's the old-fashioned matter of how one should cite various kinds of sources.  That much is easily accomplished, and I can always tell them to consult the Chicago Manual of Style when in doubt about formatting.  Then there's the larger issue, related to doubt: when should one cite?  The traditional answer that I stand by is "When in doubt, cite."  But how do you explain this to students who do not yet recognize your version of common sense?  I'm trying to think of every situation, reasonable or not, that students could bring up.  Here's what I've brainstormed:

• A short phrase of two or three words involving technical or abstract vocabulary that they wouldn't have thought of on their own.  "A good idea" is not a phrase that one needs to cite, but "a trenchant paradigm" might be.  The latter phrase is also ugly as hell and likely a smokescreen for a bullshit artist, so it throws up more than one red flag for me.
• An idea or observation that needs a bit of explanation, even if it is phrased in the student's own words.  As much as most pseudologists are familiar with Benedict Anderson's idea of print capitalism and the effects it had on creole nationalism, I'll eat my hat if most college students know that.  Talking about that stuff without clearly citing the page numbers of Anderson's book so that I can fact-check an argument might not be plagiarism, exactly, but it's shoddy practice.  (Not acknowledging Anderson as the source of the idea at all — that would be plagiarism.)
• Then there is the occasional student who thinks that zi can copy entire pages of text wholesale, as long as the source pages are clearly cited.  What's a good way to explain to a student that zi must simultaneously cite sources clearly and write for hirself?  I imagine this would be confusing to at least some people, especially the overly cautious ones who distrust their own instincts.  Should I just forbid block quotations of more than three lines?
• Web pages.  Oy.  I would like to forbid my students from citing them at all, but of course this idea is increasingly troubled by digital access to peer-reviewed scholarship.  Even the idea that some sources are inherently less trustworthy than others can be hard to work with, since pseudologists frequently engage with things that people say and write that are verifiably inaccurate — we need to study things outside of peer-reviewed scholarship in order to do our jobs.  Is there any practical and brief way to explain to students how to be wary of the internet without throwing the baby out with the bathwater?  How do you make undergrads wary of factual truth-claims without making them paranoiac?

What other craziness am I missing?  And what say you, my esteemed colleagues, for solutions?