In 'The Wizard of Oz' what do the witch's marching guards with the deep voices keep chanting? Sounds like "o-re-o".

They are chanting oeo oeo. According to the musical (live stage version that is) that my brother was TD for, when they asked what it meant they said it's a loose translation that means "Oeo oeo," so according to that it doesn't really mean anything at all.

I heard they say something along the lines of "Oh we loathe the old one" alluding to the witch.

"All we owe, we owe her."

McG is correct, and the stage version is different from the movie...

RND, I do not believe McG is correct, at least from the point of view of the movie. Go to this following link:
http://www.imdb.com/title/tt0032138/
(scroll down to the FAQ section).

It alleges that indeed the screenplay was written as "oeo", and really means nothing. It also lists a number of things people think it means. I went back and watched that section of the movie, and I could make my ears hear every single one of them. I defintitely agree with what that website says about the meaningless chant being an "audio ink blot".

Another site that also verifies the screenplay has the chant as meaningless syllables:

http://thewizardofoz.info/faq15.html

This is what this script site says.....

(*THE CHANT OF THE WINKIE GUARDS*)

Winkies
Ooo - eeeee - hoo! Yooo - ho! Ooo - eeeee - hoo! Yooo - ho! "

http://www.wendyswizardofoz.com/script12.htm