7 - 21 • Enforcement of camouflage, noise, and light discipline. • The conduct of required activities with minimum movement and noise. • Priorities of Work. d. Security Measures. • Select terrain the enemy would probably consider of little tactical value. • Select terrain that is off main lines of drift. • Select difficult terrain that would impede foot movement, such as an area of dense vegetation, preferably bushes and trees that spread close to the ground. • Select terrain near a source of water. • Select terrain that can be defended for a short period and that offers good cover and concealment. • Avoid known or suspected enemy positions. • Avoid built up areas. • Avoid ridges and hilltops, except as needed for maintaining communications. • Avoid small valleys. • Avoid roads and trails. e. Occupation (Figure 7-9). (1) A PB is reconnoitered and occupied in the same manner as an ORP, with the exception that the platoon will typically plan to enter at a 90 degree turn. The PL leaves a two-Ranger OP at the turn, and the patrol covers any tracks from the turn to the PB. (2) The platoon moves into the PB. Squad sized patrols will generally occupy a cigar shaped perimeter; platoon sized patrols will generally occupy a triangle shaped perimeter. (3) The PL and another designated leader inspect and adjust the entire perimeter as necessary. (4) After the PL has checked each squad sector, each SL sends a two-Ranger R&S team to the PL at the CP. The PL issues the three R&S teams a contingency plan, reconnaissance method, and detailed guidance on what to look for (enemy, water, built up areas or human habitat, roads, trails, or possible rally points). (5) Where each R&S team departs is based on the PLs guidance. The R&S team moves a prescribed distance and direction, and reenters where the PL dictates. • Squad sized patrols do not normally send out an R&S team at night. • R&S teams will prepare a sketch of the area to the squad front if possible. • The patrol remains at 100 % alert during this recon. • If the PL feels the patrol was tracked or followed, he may elect to wait in silence at 100 % alert before sending out R&S teams. • The R&S teams may use methods such as the "I," the "Box," or the "T." Regardless of the method chosen, the R&S team must be able to provide the PL with the same information. • Upon completion of R&S, the PL confirms or denies the patrol base location, and either moves the patrol or begins priorities of work. f. Passive (Clandestine) Patrol Base (Squad). • The purpose of a passive patrol base is for the rest of a squad or smaller size element. • Unit moves as a whole and occupies in force. • Squad leader ensures that the unit moves in at a 90 degree angle to the order of movement. • A claymore mine is emplaced on route entering patrol base. • Alpha and Bravo teams sit back to back facing outward, ensuring that at least one individual per team is alert and providing security. g. Priorities of Work (Platoon and Squad). Once the PL is briefed by the R&S teams and determines the area is suitable for a patrol base, the leader establishes or modifies defensive work priorities in order to establish the defense for the patrol base. Priorities of work are not a laundry list of tasks to be completed; to be effective, priorities of work must consist of a task, a given time, and a measurable performance standard. For each priority of work, a clear standard must be issued to guide the element in the successful accomplishment of each task. It must also be designated whether the work will be controlled in a centralized or decentralized manner. Priorities of work are determined IAW METT-TC. Priorities of Work may include, but are not limited to the following tasks: