1. Do they also mark where the Cox cable runs? They have marked everything but Cox.
In my case they just mark where they want to avoid (i.e., gas line). They typically know where they want to run the fiber already. Before they run the fiber to your house, they probably have already done tons of work in your area.
2..If I am not planning to order the Gigablast service, will any cabling have to be put in my yard?
No, unless your house is one of the house with the pedestal (usually out in the front yard), the rectangular beige looking plastic structure (the pedestal has your cable stuff in it already). Each pedestal can serves up to several houses. Only when you are ready to order the service will Cox come out to pull the fiber from the pedestal to your house. Your house typically has a conduit to the pedestal already, they just have to pull the fiber through.