Ok.. for example... I put vickie in a scene... cool... then, say, the dragonfly, (Everyone knows the dragonfly), fine.... then I move vickie x axis 2.xxx units.... I now have a vickie with  dragonfly  wings sticking out her ears, among other things. I'm sure that a dozen of you have had an accidental laugh over something like that. Funny?... yes.  Annoying?... as hell.
  what I'm trying to put across, and ask; is there a means, short of rewriting Daz, to define objects as impenetrable? and, if not, why?  Game engines do it as a matter of course, why not the other App's?  Lou.

What you are referring to is called "collision detection" and it is very processor intensive to do it right.  If you were to look at a video game closely the collision rarely touches or will slightly overlap. While it is possible to do with a plug in I doubt it will be a part of the core product because the processing requirements would raise the bar of who could use the software.

You can do it only by eye - though if you have the AlignAce plugin that can help placing one item touching another (not always - it looks at the boxes that enclose the items, so protrusions will confuse it). Switching to Hidden Line display (from the Viewport options menu - the triangle button next to the Camera/View list) may help.  

Thanks for the replies. I suppose I knew that it was like that, but it was a hope that somebody had written a plug in. Meantime, I hadn't explored the hidden line display... I'll give that a look.  If I do run into anything like a collision detection plug-in, I'll post it. Lou.