I am not familiar with the term "sock". There are graveless systems in which the field lines are wrapped with a permeable system such as styrofoam. This allow the lines to be put into a trench with the addition of gravel. Given the right conditions, these systems work successfully, however they are subject to the same type of failure as a traditional system. The soil in the trench must also perk in order for the water to be absorbed. It would also seem to me that the capacity to store water during surge periods is not as great as a traditional system. As a result you may need to add more feet of line to compensate.