A withdrawal may be necessary when a defending force is outmatched or on disadvantageous ground. But it is usually important to cause as much damage to an enemy as possible. In such a case, the retreating force may employ a number of tactics and strategies. These are to slow an enemy's progress. This could include setting mines or booby traps during or before withdrawal. Sometimes ambush by a small force can slow or stop an enemy advance. Also, leading the enemy into prepared artillery barrages, or the use of scorched earth tactics.