Re: 6" by 6" cedar posts and risk of rotting when sitting them on to of concrete foot
The posts should not be in direct contact with the concrete, as they will wick moisture from the concrete and rot from the bottom up. Typical post bases have a metal plate that holds the posts 1" above the concrete so that they stay dry.
Dry stacking stone around the posts will slightly increase their susceptibility to rot, however because it's dry stacked, the posts will be able to breathe so that any moisture that gets in will eventually find it's way back out.
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