I Used to work at a zoo which had a man-mad bog/pond, it was blasted out of the rock many years before. and the thing actually held water, it was more of a fen, because it was filled by snow melt/rain, and was probably about 20'x20' 4 feet deep, and it supported a large diversity of native reptiles/amphibians etc, until someone released their pet goldfish into it! I used to love rowing into the middle of it during my lunch breaks, the water was fairly clear, there was some underwater vegetation that would form a mat across the deeper end, it wasn't peat, but it did stink if you disturbed it! I could watch red spotted newts in their aquatic phase swimming through the vegetation, the males would do these elaborate mating dances it was amazing, I had never seen them in they're aquatic phase, they were twice as big as their "eft" phase, and had flat paddle like tails, It was a lovely safe haven for these creatures to mate and lay eggs, until the goldfish came, in two years time the fish bred explosively until they overran the pond, you could here them mid day sucking air from the surface because there was just to many fish, not enough oxygen, and of course, the newts left, or were eaten, it was tragic. they did finally restore the pond, and got rid of most of the fish, but could never get all of them out and the newts never came back. just goes to show you how quickly invasive species can destroy an entire ecosystem.
As far as building the bog it does seem the best option to me. Is the site fairly wet? do you pipe water in? hope it all works out and you have a lovely safe haven for the frogs and maybe salamanders.

You nailed it. A bog is the cheapest garden to build and the cheapest to maintain. It requires no cleaning, no watering, no nothing. And stuff grows like crazy in it. The plant roots suck up that moisture. I keep toying with the idea of a pond where my bog garden currently is, but a pond is so much more expensive, complicated, and time-consuming than a bog. Many people seem to be naturally shy of the idea of a "bug-infested, mushy, swampy" area as a garden. They immediately wrongly assume there will be snakes, quicksand, and mosquito-borne malaria. Humans have been dredging and avoiding swamps throughout our history, so we have an ingrained cultural aversion to bogs. But nature loves them. Plants and wildlife love them. They serve important functions in the ecosystem. And I think they're beautiful. They make the perfect gardens. There should be more of them.