Possible Clues:

• Defensive action
• Where van's often on line with its occupant not in the van
• Military detachment in the back
• Troops protecting back of military formation
• A rare drug distributed as a means of defence
• Stern rail employee's defence
• Conservative element of a community
• Look after dope upset about a conservative faction
• Body of troops protecting back part of army
• Conservative faction bring up "misuse" of a drug