The simplest gar fly I know of involves fraying out some nylon clothesline of poly rope (anything with fine frizzy strands that will tangle in the teeth) and tying it to the hook streamer style. Some people even cut the bend of the hook off and just use the shank, relying on the rope fibers to hold the fish. They are solid bone from the eyes forward so a good hook set is extremely difficult to achieve. Me? I just use regular streamers and don't mind the fact that 95% of them spit the hook before I have to deal with the teeth. I still get the fight and since I would have turned them loose anyway the end result is the same.