I'm building a shallow pond using plastic sheeting 10 mil thick and covering it with 2 ft of dirt. Anyone has any experience with that?

It would be nice if you had a softer underlayer under the plastic........fine sand is one or actually old carpeting works well. I don't know why you are covering it with dirt unless you are expecting foot traffic into the pond, then again I'd be looking at clean sand instead of dirt to reduce the cloudiness from the dirt. the more clay, the harder it will be to clear the pond. What about circulation and aeration?

As they make and sell pond liners, made to do what you want. I think I'd look into getting one.

If you put fish in the pond be aware of predators! We had mountain lions coming to our pond at night and eating the trout.