Where we are renting at the moment is in a fairly unprotected area (still being built) and when it's really windy, the fence wobbles. It's colourbond and concreted in(?) but the whole length of fence does like a wave as the wind hits it. It doesn't surprise me that wind would be able to do that if the posts weren't particularly strong. Are you able to get different posts? Excuse ignorance, but are there something like red gum posts that would be stronger?
Ray.