Separable word"撤" and "防" can be combined as one word, or be used separately with other elements inserted.一下子撤了防，给了敌人可乘之机。
All of a sudden, the defense was withdrawn, giving the enemy chance to take advantage of it.
目前局势紧张，暂时撤不了防。
At present, the situation is tense and we can't withdraw from a defended position for the time being.
你们什么时候撤的防?
When did you withdraw from a defended position?