Thank you for the permanent guide lines. After positioning a guide line how can I place another guide line at a given distance parallel to the first. If I move it nothing stays behind. If I grab another one from the side - place it on top and then move it they both move (or the one cancels the other out). I have read through the help center and don't see anything that deals with this. I have also tried various combinations with the ctrl, cmd and shift keys to no avail.
Got it - thank you Eduardo. And I also learned that you can Cmd-D + alt on the fly with walls. I have only ever selected them first and then typed Cmd-D + alt - which I couldn't do with the guide line