I am needing to dig a hole and mount a pole for a friend of mine near his pond. The pole will have a very large bird house on top so it will catch some wind. He wants it near the bank of his pond, I am just not sure how far the edge of my hole should be from the bank. The pole is 3 inch square and will be 15 foot high, the martin house on top weighs near 100 pounds. Obviously I don't want to be too close and have it blow over due to soft soil. I know nothing about ponds or excavating for that matter and didn't know if there is a general rule for such things?