Tom, I'm sure ML will comment soon on the bale thing.
Regarding you hitting a spring, from what I've read here on the forum, it may not be good news. A lot of the members have experience with that.
You may want to create a new topic in this general category, maybe under "Selecting a Site" or "Soil," or maybe a new thread in this sub-category to make sure you get some pertinent answers.
As far as artificial structure, my pond is 6-7 acres, and everytime I feel I've done a lot of structure placement, I know I should do more. People do use old cars, but I don't know the procedures; I would guess you would remove anything containing hyrdrocarbons, or remnants of hydrocarbons. Two or three cars would be good, but ten to fifteen would be better.
