If it was an enemy turret that the player didn't control but shot at you, you could probably create two tanks overlapping eachother, one shot a laser doing zero damage and another one that shot. It would appear to be aiming at you with the laser. However to make it the one you control, is not solid flag available for turrets? Because if so, just make the whole func_tank render as solid and use a masked texture for the laser beam. Or additive.