Diana, thank you very much for that informative post! That's exactly the kind of thing I was hoping for. (Thank you wicca and armedbiggiet, too!)
So, I accept the fact that moving water and air bubbles are what keep the ponds from becoming stagnant, but I just figured that maybe having photosynthesizing plants might have helped to offset that. Maybe not? I did already plan on doing regular water changes, but I don't know if that's enough to replace the need for moving water or not.
At any rate, I'm now thinking I will have to setup a solar cell. We already have one that powers up all of our lawn lighting, so I'm going to see if I can tap into that. I don't really know if it will provide enough power, but I'll at least look into it. Otherwise, it looks like I'll be setting up a new solar cell, just for this project. (I knew being an electrician's apprentice when I was young would come back to benefit me later on!)
I was already planning on stocking each tub with gambusia (mosquito fish) and maybe some least killifish. These are both 2 kinds of fish that I have a seemingly infinite supply of, as they are found in the wild all around me. If I didn't get these, I was inevitably going to have a mosquito problem. But now I'm wondering, if I'm going to have moving water, will these fish be able to eat? Mosquito's aren't going to lay larvae down on the water if it's moving, right? So doesn't that negate the need for the fish?
Diana, I like what you said about burying the tubs in the ground for temperature stabilization. That's something I don't think I would have thought of on my own until it was too late. That's one of the many reasons why I knew I had to start a thread, because dang it, I just don't know everything!

But I'm starting to think now, if I'm going to have power running out there anyway, maybe I should just plumb all the tubs together into a recirculating system, and connect an inline heater to it during the winter months. I don't know how practical that is though?
Of course, if I plumb it all together, that opens up another possibility: I could connect a rain barrel to the reservoir with an auto-top-off kind of thing, which will make me feel even greener!
As far as blocking the ponds off from critters, that's definitely a concern that my brain hasn't even approached yet. We get a lot of critters through our yard, from raccoons to armadillos to birds of prey to our housecat, and more. I was kind of hoping this could just be done in an innocuous sort of way, so that it just wouldn't be appealing to these critters. I didn't expect to have any colorful or large fish, that would catch a predator's eye or anything like that. And plus, I have a large, natural pond back there that I would think would be way more interesting to these critters in the first place. I mean, that one's stocked with turtles, large fish, all kinds of birds, etc.
Then, lastly, the placement under the sun. As I said before, Diana, I have the option of placing these tubs under just about any combination of shade or full sunlight that I would want. Are you saying that I would be better off having a good solid few hours of 100% pre-noon sun, then the remaining hours under dappled sunlight? Or are you saying I would be better off keeping them under constant dappled sunlight all day long? Because both of those options are easily accessible to me. Obviously, like you said, since the tubs will be smallish, direct sun could heat that water up in no time, so yeah, keeping it under shade or dappled sun during the hot hours would be a good idea.
I'm actually going to Lowe's this weekend to see what I can come up with as far as tubs. I still think pond liners will end up being the best option, but I'll keep my options open. I wouldn't even mind a masonry project, I suppose, if it will end up being cheaper to make concrete ones. I guess I'll soon find out.
Thanks again, guys, and if anyone else would like to chime in I'll be your best friend. Anyone who provides me with beneficial info for this project will get put on my RAOK list, as I expect to eventually have more plants than I will need, and plan on giving excesses away here and on the other forums.
