Look into getting some pond liner from Lowe's or another source. Then you can shape the pond exactly how you want it. Remember, if it is very shallow with no areas deeper than at least 3 or 4 feet, even FHM would be liable to winter kill with no deep water areas during ice over. Shouldn't affect the frogs and tadpoles though. I have found lined ponds do not support near the biodiversity of amphibians than a earthen pond does though. I would find an area that is natural moist and just excavate it a bit... I recommended the mudminnows and topminnows as that is there exact niche... You won't need to stock many of them. If you need a source for a handful, I can give you a place to buy them. Just a half dozen to dozen would do.