My friend and I have spent many nights in the bayou's and swamps of south Louisiana, bowfishing for gar. It's a lot of fun, but they're not as easy to get as it might seem. Their hide is really tough and slick, and on the most common sized ones (2-4" diameter) the arrow point will just glance off unless you hit in right in the center. If I remember correctly, we averaged about one fish for five shots. But we drank beer and had a blast until the sun came up or the Q-beam battery died out, whichever came first.
If quantity is what you're after, a multi-pointed spear is a better tool. I know of a guy who welded a spear head; it was about six inches wide, had four or five points, with barbs made from nails. The points had been ground very sharp, and not many gar ever got away. He could fill an ice chest easily in a night. I've always wanted to run into one of the huge alligator gars, which can get to six feet long, and weigh over 200 lbs., but the biggest I've ever gotten was around 5 lbs. Our bowfishing setup was geared to handle one of these dinosaurs if we ever got lucky enough; 90# test line, wrapped around a bowfishing reel, but only enough string for a long shot, (to the end of the light spot, about 20 yds.) then the end was tied to a plastic liter bottle which was velcro'd to the lower limb of the bow. If we ever shot something huge, it could pull off the bottle and we could keep track of it, and use whatever means necessary to kill it. There was usually a handgun in the boat.
By the way, gar can be good eating if you know what to do with them. Clean, debone, grind, and make gar fish balls, season and deep fry. I'm sure my cajun neighbor from down the bayou, SOUTHLA1 has tried this.