There is a well known dictum that a lot of rabbinic enactments were created to 'create a fence' around the major sin; the idea being that if someone does something that would be Biblically permitted but might lead them to wind up doing something Biblically prohibited, better to make the secondary act prohibited, so that they won't wind up doing a Biblically prohibited act (I'm trying to come up with examples, but the only one I can think of offhand is that you're not allowed to tear off leaves from a tree because you might wind up tearing off branches from the tree - feel free to edit this if I got this wrong).
However, there is also an indication (if memory serves) that when we prohibit a tertiary act, we can be lenient in such a case. I.E. If we are worried that someone doing action Z will wind up doing action Y, and as a result will wind up doing action X which is biblically prohibited, we make actions Y & Z rabinically prohibited as well; if someone were to have a doubt about action Z, we have room to be lenient, because this is a 'fence within a fence'.
I then have two questions: 1) How far down are we obligated to go? In theory, you could add multiple layers of 'fences' (which ultra-orthodox people tend to do, for fear of coming anywhere near a prohibited act), but I can't imagine that these rulings are/should be binding on everyone who wants to follow G-d's law. 2) If someone were to break a tertiary (or a quaternary - yes, that is how you describe something at a fourth level - etc.) prohibition, are they liable for similar punishment as the primary or secondary prohibition?