wrote in message
...
Am wanting to build a double gate made of treated wood - 2x4's and 1x6
x6'.
have a 10' opening, so 2 - 5' sections. I think these gates will be a
bit
heavy, so I am wondering if I should use 4x6 posts to support these
things
rather than 4x4's? I plan to cement posts in ground about 48" (frost
line
here is 42")

Cement around treated lumber is a bad idea, unless you like wobbly posts.
Treated lumber shrinks long after the concrete cures.

I second the idea "Joe" has.