SRS -

In the soil we have around here, a too long metal post isn't a problem, if it's just one or two posts. You just drive them a little deeper. Of course you really should have a suitable "post hammer" and opinions vary on whether you really need the customary concrete anchoring with a steel post - especially one driven "extra deep."

If you have rocky soil, of course, once the post hits the first significant rock the post won't go any deeper, so hammering just makes the post shorter by crumpling up the top end. A couple of inches "improvement" is about all that's practical though, with "normal" driving tools - and it may look really messy when you get done if you appy this "method."

John