Originally Posted by nealtw
What do you think is holding your post with a lump of concrete on it?
I have seen a fence blown over with a good wind, concrete and all, the soil was saturated , almost mud.
I have to think about this.
With concrete in a hole the soil is already compacted and the concrete has more surface area to grab the soil but for low fences just soil may be enough.
I'll have to look inhttp://www.amazon.com/Civil-Engineering-Reference-Manual-Edition/dp/1888577959
the next time I'm at the library.
Probably the properties of the soil, the fence height and the post hole depth are the main considerations.