It is really simple, all you have to do is put in an 'ai_relationship' entitie and have the object being the turrets and the target being '!player'. You must have the ! before player or it wont work. It should also work with any other person, striders, combine, ect.
The target can be a npc class name, such as npc_combine_s, npc_antlion, ect. Or it can be a npc's name.