I don't think you need to really walk the line. As others have said keep the bucket low - I usually keep mine at a slight angle upward so that if I do hit something, it rides up. Go very slow, and always keep an eye all around you. Make sure you are prepared for getting swiped by thorns, and running into wasps. Do your first pass on the outside limit from the fence so you don't hit it. Also double check all the pins to make sure they are wired in and you don't get them pulled out. Check for any dangling hoses etc that might be caught on something. Keep in 4 wheel drive, and watch your temps. You might want to clean the screens before each pass. Where outside of DC are you? I'm up in Alexandria, but my place is in SC.