It sounds like you were into dogs, sharks or hake. Often times they will bite the back hook off only. Bigger ones the whole thing. But I do have kings saw the leader off on their teeth sometimes too but not often. I use straight 25 green Trilene Big Game line and always use fixed hooks. I caught an 80 pound halibut on that stuff so I know it's strong stuff. Constantly check your leader for nicks. Often times a fish will nick a leader between the hooks. I also tie everything up with snap swivels so you can change leads and leaders fast. I tie a barrel into the middle of my leaders to prevent twist and as a last catch of seaweed sliding down your line before it gets to the bait. I mostly motor mooch on feeding kings and simple fish tailing of the boat will change the depth of your line.