What's a good estimate on the amount of time to install rock. Putting in a bid to "touch up" about 850 square feet of pond rock that's been neglected for several years. I'm thinking about 4 tons of fresh rock, which the rock guy says should cover 400 square feet, 2" deep. Am I correct that this should easily freshen up about 850 square feet? What sort of time should I factor in whan putting the bid in?