One of the most common pieces of advice on Pond Boss is, "No trees on the dam!"
That mostly applies to newly constructed dams where small trees are starting to get established on the dam. People need to eliminate them before the tree roots start to damage the clay seal in the core trench of the dam.
You are obviously in a different situation, but the same principle applies.
There are also stories of people cutting down large trees on their dams and it makes their leaks worse. The living tree would only "thief" a small amount of water. However, once the tree roots decomposed there was an easy path for water to migrate through the dam.
Are there any trees adjacent to your pond that are going to be cut down to match the final design of the "plan" for the pond and the surrounding area? If so, and you are going to perform any mechanical work on the sides of your pond, you might consider cutting those trees down first, so they aren't working to pierce any good pond seal that your worked to create.
