如果低吼的时候，前后腿是前倾的，表示主动进攻型，就是他很aggressive，比较有dominance 控制欲，那他的obediance training需要加强。如果他的腿是往后坐，身体试图要躲避，但是还是发出低吼的话，表示passive aggreessive，表明他怕见到陌生的狗或人，这种状态说明他需要加强与各种狗各种人的social，让他习惯不同的场景。
就你说他小时候比较胆小，常找你寻求保护，说明他是有些passive aggressive的。
无论何种情形，这种低吼的状况还是要及时纠正。有一个办法是Dr。McConnell讲的，可以借来用用。当你看到Apple对那个狗狗发出低吼的时候，你可以用腿往旁边挡开他的身体，让他瞪视着对方的眼神与对方错开，也许可以缓解这种进攻性。这个方法对丘丘非常奏效
当狗狗打架的时候，千万不要用自己的手去劝架，最好拿根棍子挡开他们，以免自己受伤。
这是有20年经验的训狗师写的文章，你可以参考一下
Dogs do commonly warn each other off with snaps or growls. These gestures are not intended as combat, especially when females react toward males. Although most of the time dogs usually work out hierarchy without resorting to actual physical combat, owners do need to recognize situations that can lead to disaster. Certain challenging postures, such as standing very erect, holding the head over another’s back, direct staring eye contact, and mounting, need to be corrected immediately by the owner.
If these postures continue to persist, owners should keep an eye out to make sure that a fight is not ready to erupt. Make clear to your dog that this behavior is not desired. Remember that gentle crooning does not dissuade undesirable behavior, but rather encourages it. Keep in mind that once dogs learn to fight, they may form a pattern that is sometimes difficult to unlearn.
