Circle hooks work great for halibut because once they’re set in the halibut’s mouth they simply don’t come out. A second advantage to a circle hook rig on a mono leader, is that the fish are much easier to release. The hook nearly always ends up in the corner of the halibut’s mouth and not inside the mouth or even worse, down the halibuts throat. So you can get a solid hook set easily. Especially if you do not set the hook. Let the Halibut munch on your bait a bit, and slowly pull in your line. Your hook will embed itself in your catch right in the corner, and he'll be non the wiser as he is swimming away, but already caught.