Weiss, congratulations on being able to maintain those trees so nicely! I thought I had a pretty high density with my plants but you take it to another level! My trees are much younger than yours and when I planted, I had people tell me not to plant so close to the house (some trees just a couple feet away) because the roots will damage the foundation; I planted anyways. Later, I thought about potential problems with gas or sewer lines at such a high density. Have you ever had the roots of your trees cause problems with anything (foundation, sidewalk, gas/ sewer lines, or septic tank/ field?