A friend and I will be visiting Monument Valley Navajo Tribal Park at the beginning of September 2011. We would like to take a jeep tour in the park with a Navajo company. (1) Are there tour companies that you would either recommend or advise to stay away from? (2) At that time of year will we be able to find a tour company at the visitor center without an advance reservation? (3) Most company's websites that I've seen require a minimum of 3 people. Will we will able to join other groups to make the minimum? Thanks.