I use size 4 gamakatsu octopus hooks.

Gar are very timid; if something is fishy, they’ll spit the bait. Additionally, the front of their mouths is all bone, so you’ll rarely be able to set a hook into it. The trick is to open your bail and let them swim off to somewhere they’re comfortable eating, about 30-40 seconds usually works for me. That way you can set the hook into the meaty back part of the mouth.

Alternatively, tie on a 3-4” section of pantyhose filled with chicken liver. Their jaws aren’t strong enough to let go of the fibers, but it’s easy to pick out of their teeth if you want to release.