A post for a fence has less structural loads on it but more shear loads; certain precautions should be taken, IMHO. Mound the concrete on top for water run-off, extend the wood post past the bottom of the concrete collar- no concrete under the post to encase it in concrete/water as it acts like a sponge, Picture figure 7 but with post going through collar and able to dry to the gravel in bottom of hole; http://www.sustland.umn.edu/implemen..._footings.html
1/3 to 2/3 post rule, depends on your location: http://www.brainerdhomeinspection.com/frosth~1.pdf
As soon as the post/concrete joint opens above grade- seal the wood (pt wood is not waterproof, only fungi/bug proofed- unless you specifically ordered it special; http://www.ehow.com/info_8535764_woo...-bad-idea.html
Notice #12 also. Lol, they are all pretty good….
This has it correct --at least on “wood post in concrete footings” area; http://www.bydfence.com/fqa.htm
Hence the “concrete collar” by adding gravel, set post (waterproofed) on gravel after turning it down in while lining to string line, add mixed concrete, trowel top bevel on exposed above grade concrete (wind helps dry collar).
No, the saturated earth will not hold any shear loads until dry. May not even hold the concrete in check.... bad idea.