Spotting mines - if you are in an area where you think mines are located, use your Obs Scope while submerged to make sure the path ahead of you is clear. (not realistic but safer)
Mines & Subnets are not in the RND layer. (jump in to correct me
) IIRC they are in the SCR layer and I think the only way to remove them is manually via the mission editor. (GW1.1a) Rather a long task.