A month after a Johnson County natural gas pipeline exploded with deadly force, the Houston pipeline company accused of failing to mark the pipeline says it tried. The NTSB says Enterprise Products failed to place markers along the route of the pipeline which ignited ferociously when a utility excavation crew punctured the line while installing power poles.  But an Enterprise spokesman says their employee tried to mark the route of the pipeline near Cleburne but could not find the excavators.  The spokesman then says the employee spoke to the contractor the morning of the explosion and was told the work was already complete.  The June 7th blast killed a crew-member from Oklahoma and seriously burned several others.