Interesting question, personally I've seen alot of things work out just fine as a <a href="http://www.billingsagriculturalfencingpros.weebly.com">corner post</a>. In Australia, we tend to have a thick clayey soil which loosens considerably as the ground dries out during the dry season. Therefore, using a bigger, heavier post was a priority, as was using concrete to help add weight when the fence tension starts pulling your posts over! I usually went with 8"-12" diameter 1/4" pipe; probably never anything smaller than 6", but that's just my personal preference. We also used "floating stays", that is, angled 2" pipe braces which seated to the post about 4' off the ground, and ran along the fence to a 2' by 2' concrete pad. This in turn had a 3/4" steel threaded rod linking to the brace and post, with a nut and washer to tighten against the post to keep fence tension. I'm not sure if this method is highly used, but it was pretty effective and eliminated the need to do much post pulling or straightening by tractor as one occasionally must do. Probably sounds a little confusing, but Patriot North America does a pretty good explanation on YouTube if you need it. Hope this helps... btw H braces are also effective, but if your soil is loose I'd try the method I described. Good luck!