Have you looked at pilings? You can get a lot of mileage from pilings without the swaying of smaller diameter pipe.

Your profile doesn't say which state you're in, but it is likely you can find a piling source in your state. Here are a few;

http://www.americanpoleandtimber.com/poles-pilings/

http://www.gulfcoastpiling.com/wood-pilings.htm

http://www.americantimberandsteel.com/poles-pilings-pilings.html