I use these. Get them at HD for under $10. The ones I got were gray...not sure if galvinized or not...

{{gwi:378426}}

What my husband does when he is not worried about a lot of stress on the post, is to dig deep, set post, then tightly tamp small rocks and dirt around post until hole is full.I believe this is the method most used by farmers as well.
Tammy

Thanks! I'll give this a shot!

Leisa

For large posts I do as Tammy said, maybe because I'm a farmer's daughter.

One year I built a wooden trellis and pushed the slender wooden ends in the ground which held well but eventually rotted. Not wanting to waste that big trellis I bought three short pieces of rebar and attached them to the trellis then pushed the rebar into the ground leaving the wood slightly above ground. That has worked well for several years.