P: Rulers when tethering

I use a lot lightroom for tethering fashion catalogue. 

I think that rulers in LR is a too poor tool. 

Rulers should be more thin and we can only move a couple of axes. I can see it in library but disappear while i try to crop the image (it would be the most useful situation to use them)

Also i really miss the possibility to overlap an image as reference for setting rulers and crop all pictures right.