I think dirt over a liner would just make a muddy mess. The little pond I built just has landscape fabric under the rock and it holds water well. If at all possible I would put rock or sand down, the deer seem to like the solid footing.
What type of liner do you use and where do you purchase them? Also, what plants are easy to establish and free of maintenance?Personally I would cover with a sand or gravel if available. If dirt is only option to cover liner, then I strongly encourage installing beneficial aquatic plants, applying pond colorants, and adding beneficial bacteria. This way you can balance the ecosystem. The Culicoides midge that causes EHD does NOT like competition. So if you have a balanced ecosystem with a high bio-diversity of aquatic insects and invertebrates you will greatly reduce the chances of EHD. I don't know personally how the Iowa DNR perceives small ponds, but the Wisconsin DNR are advocates for wildlife ponds to help improve wildlife abundance on properties.
What type of liner do you use and where do you purchase them? Also, what plants are easy to establish and free of maintenance?
My recommendation would be to also plant the shoreline edges of the pond with some common arrowhead and/or pickerel plant to help filter the water. These plants also won't encroach into the pond like a cattail would.I've used small water tanks like you buy at the feed store for cows. Don't think the deer ever accepted them.
This year we got a dozer to dig a hole about 5 feet deep. It's about 20' x 40'. Rain filled it up in a couple of months and it held water during the summer drought. The deer really use it and I think it was a great addition to the farm. It's on the edge of a 2 acre food plot, clover.