We are currently putting in an all concrete pre-fab dock. Originally I was going to do a treated wood one with telephone poles as footers, even bought a half dozen used poles.
Then we saw an all concrete dock that some friends of ours had put in in and decided to pay a little extra for a maintenance free dock that should last for a long long time.

Ours will be 24.6' long 10' wide, we wanted to get it out far enough so that if we or the kids ever put a diving board on it the water will be plenty deep. It drops off into 15' pretty fast.

[Linked Image from i.imgur.com]


The footers for the columns are 36" round by 5' deep


[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]


Poured columns a few days after putting footers in

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]

[Linked Image from i.imgur.com]


The pre-fab beams and deck sections are all built and will be coming in on a big truck with a boom as soon as the rain here slows down enough for the dirt to dry out for the truck. Should be within a week, then all that will be left to do is ad a stainless steel ladder, put a couple short fish structures under the dock and let the pond fill up.