On Mon, 15 Apr 2013 16:36:31 +0000 (UTC), Andrew Gabriel wrote:

One comment I would make - make sure the holes have flat bottoms
with good square corners where the base meets the side. Many years
ago, I dug a couple of holes for a neighbour, and I did as I said
here. The holes he dug were shaped like someone had pushed a football
into the soil. A year later in a strong wind, all his concrete lumps
rotated in their holes leaving his bit of the fence leaning (none of
the posts snapped), and the ones I did were still upright.

Sounds more like they wern't deep enough. Rule of thumb is 1/3 in the
ground as is above. 6' fence uses 8' posts with 2' in the ground.

Admitedly a square lump is less likely to rotate than a ball (in socket).

--
Cheers
Dave.