Im new to this so sorry if it sounds dumb but try ripping of the ability the missile defender has, located in data\INI\Weapon.ini
Code:
;------------------------------------------------------------------------------
Weapon MissileDefenderLaserGuidedMissileWeapon
PrimaryDamage = 40.0
PrimaryDamageRadius = 5.0
ScatterRadiusVsInfantry = 10.0 ;When this weapon is used against infantry, it can randomly miss by as much as this distance.
AttackRange = 300.0 ;Extending this range, allows the special ability to work better.
DamageType = ARMOR_PIERCING
DeathType = NORMAL
WeaponSpeed = 600
ProjectileObject = MissileDefenderMissile
ProjectileDetonationFX = WeaponFX_RocketBuggyMissileDetonation
RadiusDamageAffects = ALLIES ENEMIES NEUTRALS
ScatterRadius = 0 ; This weapon will scatter somewhere within a circle of this radius, instead of hitting someone directly
DelayBetweenShots = 500 ; time between shots, msec
ClipSize = 0 ; how many shots in a Clip (0 == infinite)
ClipReloadTime = 0 ; how long to reload a Clip, msec
AutoReloadsClip = Yes
FireSound = MissileDefenderWeapon
WeaponBonus = PLAYER_UPGRADE DAMAGE 125%
AntiAirborneVehicle = Yes
AntiAirborneInfantry = Yes
; note, these only apply to units that aren't the explicit target
; (ie, units that just happen to "get in the way"... projectiles
; always collide with the Designated Target, regardless of these flags
ProjectileCollidesWith = STRUCTURES
End
Just my 2 cents