Copenhagen Zoo - Elephant herd

Toddy, do you mean something like this:
ZooLex Picture 21

Chester mostly uses ha-has, but there is a small section of poles disguised as tree trunks in the area where it's not really possible to create a slope.

http://www.zoochat.com/581/asian-elephant-exhibit-56731/

This is what I meant by Miami Metrozoo's countless moated paddocks, but at least the enclosures at that zoo are large and the obstructions are zero.

Is this the primary viewing for the elephants?

i think steel poles and cables offer urban zoos in particular the best opportunity to contain elephants and maximise space utilisation. the reach of their trunks out of the enclosure can be curbed by electric wires.
as people have pointed out moats use a lot of space.
and though the give an un-obstructed view essentially the animals end up being further away. unobstructed views can of course be obtained by elevating viewing platforms.

I think a mixture of methods is best when desplaying elephants.

Something like the above further spread out and used as a cable barrier, but veiwable through a forested area to give the impression of veiwing the animals in the wild. then round the path an open vista using a dry moat and built in the elephant house structure a veiwing platform.