i agree with richard in looking into the tankmates...gars can definitely set off other gars, but usually not into that much of a jump...gars seem to set off other gars in a rapid downward/away dispersal as opposed to upward (at least in my observations).
i think if a large gar wants to move upward it won't matter if it is 2" or 5"...as i've had some big gars jump and easily clear wherever the top of the tank would be, AND move the top of the tank to end up on the floor...hence the weighing/taping down of covers now.
and as for picking on you...we're really just giving advice here, however, given the leeway of hazing rituals, this is the second time it's happened to you
don't worry, it's nothing on the level of thinking topping off a tank is a water change/keeping a large Cuban gar in said conditions 
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--solomon