Here, let's know what we're really discussing: On a practical note, when the adult moths will fly a couple of miles to find a mate or an appropriate host crop for their eggs, will 20 or 50 or 100 feet of isolation space make any real difference? Probably not IMHO. Your best bet is heavy use of Bt powder during the summer. I spread it around my garden on various crops about every 10 days. Alas, I admit that I do not get black swallowtail or monarch larvae in my yard, but I also don't have problems with cabbage worms or corn earworms or tomato hornworms. Unless I forget for at least a month. The beauty of Bt is that it's safe, cheap, and easy to apply. I use my "Dustin' Mizer" and do it on a windy day for maximum dispersal. Biologic warfare at its best. Here is a link that might be useful: Corn earworm aka tomato fruitworm

Basically that is what I said...........including that that the roots will probably not be an issue of danger to the line. I certainly did the very same thing, but I'm rural and kept them away from any riser situation where excavation is far more likely. However, watching a water line come through closer to town, I saw an whole allee of mature trees die a horrible death when the utility companies trenched a line in the easement nearby, and severing half of each tree's major roots. The property owners had even hung a little sign on the trees for them to be careful. ;-) But with a narrow easement the contractors had little leeway to do any detouring, even if they were prone to and I doubt they were. It's your call to make and without a crystal ball, no way to really tell if that situation will ever happen. Personally I am an admirer of the big trees, so many people won't plant anymore.

hey mary ... how about some relevant facts.. how big is your yard ... soil type... wind issues ... perhaps a picture ... you really havent given us much to work with here .... i love oaks.. they grow surprising fast ... and are extremely strong in the long run .. avoid all plants that claim to grow super fast ... give us anything else that will help us limit a discussion of the flora and fauna of utah ... ken

don't prune too much or you wont get a good breba crop next spring. but since you're in zone8 Georgia, you still have a month or two before it gets cold, giving you some leeway to do a little pruning, and giving the trees some time to regrow a bit before it gets too cold and they go dormant for the winter.