text: Chapter 17
  constructed obstacles and some demolition obstacles. During a retrograde, including security force passage,
  the requirement for obstacle control will typically be increased.
  17-6. Units must weigh the risks of employing obstacles, especially lethal obstacles, near civilians and
  consider enhancing marking and restrictions to mitigate their risk. Units rely heavily on command-detonated,
  self-deactivating, or nonexplosive obstacles to deny the enemy freedom of movement and provide close-in
  protection. Denying enemy freedom of movement may involve disrupting the transportation of weapons and
  supplies and the emplacement of explosive hazards along roads or routes. Networked munitions are ideal
  when conducting countermobility in support defensive efforts around base camps and other critical fixed
  sites and infrastructure.
  17-7. The conduct of countermobility typically involves engineers and includes proper obstacle integration
  with the maneuver plan, adherence to obstacle emplacement authority, and positive obstacle control.
  Combined arms obstacle integration synchronizes countermobility into the concept of operations. Because
  most obstacles have the potential to deny freedom of movement and maneuver to friendly forces and enemy
  forces, it is critical that units properly weigh the risks and evaluate the trade-offs of employing various types
  of obstacles. Countermobility includes the following tasks:
  * Site obstacles.
  * Construct, emplace, or detonate obstacles.
  * Mark, report, and record obstacles.
  * Maintain obstacle integration.
  TERRAIN REINFORCEMENT
  17-8. Units reinforce terrain by employing existing, reinforcing, tactical, and protective obstacles to prevent
  the enemy from gaining a position of advantage. They take full advantage of the natural restrictiveness of the
  existing terrain to minimize the time, effort, and materiel needed to achieve the desired effects and offset the
  limited, available quantities of scatterable mines and networked munitions.
  EXISTING OBSTACLES
  17-9. Existing obstacles are inherent aspects of the terrain that impede movement and maneuver. Existing
  obstacles may be natural (intractable soils, rivers, mountains, wooded areas) or manmade (enemy explosive
  and nonexplosive obstacles and structures, including bridges, canals, railroads, and embankments associated
  with them). Although not specifically designed or intended as an obstacle, structures may pose as an obstacle
  based on existing characteristics or altered characteristics that result from combat operations or a catastrophic
  event. Structures such as bridges and overpasses present an inherent impediment to mobility based on weight
  and clearance restrictions. Existing obstacles are shown on the modified combined obstacle overlay (also
  known as a MCOO) developed as part of the IPB process.
  REINFORCING OBSTACLES
  17-10. Reinforcing obstacles are those manmade obstacles that strengthen existing terrain to achieve a
  desired effect. For U.S. forces, reinforcing obstacles on land consist of land mines, networked munitions, and
  demolition and constructed obstacles:
  * Land mines. A land mine is a munition on or near the ground or other surface area that is designed
  to be exploded by the presence, proximity, or contact of a person or vehicle (ATP 3-90.8/MCTP
  3-34B). Land mines can be employed in quantities within a specific area to form a minefield, or
  they can be used individually to reinforce nonexplosive obstacles. Land mines fall into the two
  general categories:
   Nonpersistent. Nonpersistent land mines are capable of self-destructing or self-deactivating.
  Land mines can be further defined as antivehicle or antipersonnel. They can be air-, artillery-
  , or ground-delivered.
   Persistent. Persistent land mines are not capable of self-destructing or self-deactivating.