Fraid you cannot better Scaffolding poles.

We have two about twenty foot apart, 8ft high. We still have to tether them
to avoid them pulling together.
I suppose that this would be unnecessary if you used enough concrete to set
them in !

We use Canes for the intermediate uprights and very strong non- stretch rope
as a top stretcher.

Regards
Pete
www.thecanalshop.com