Chop the back from the tail to the head using a hatchet. Take the gar and hang from a hook. With a sharp knife, cut through the folds of the scale behind the head. Take a pair of catfish skinning pliers and pull the hide off. Make sure to wear gloves when doing this, the shell is very sharp.
Another way to skin a gar is to shell it out with a sharp knife. You still chop the back from the tail to the head, then you just pass your knife between the shell and the meat.
Warren