When I was first working my farm up to something usable, I used my Christmas vacation to do my fencing, weather permitting.
I liked working in the fresh air and preferred it to the heat of summer.
What I found interesting was that when I set my posts, I would set them in concrete and the top would flare slightly at ground level.
In the late July, August time frame, the flare would be above the ground level and the drier the higher. Also it never went back to where it was through the winter cycle. Sometimes it would be 4" above the surface after a few years.
I didn't pay attention to the moon, not knowing any old sayings, but I do live on Houston Black Clay which a local Civil Engineer stated: "Soil is unsuitable for dwellings and roadways." i.e. due to swelling and shrinking as the moisture level moves about.
Course we (and all the other inhabitants) live here and we have both. Foundation companies make a ton of money and the highway department can't keep up with the dips in the road.