Missles and jumping

I need a little help trying to make missles that will miss if its not near you. I tried using a projectile but that doesn't work too well is there another way? Also im trying to do triggers for a unit when its in the air it can't be attacked by ground units but so far I can't get it to work any ideas?

projectile didn't work? mmh. set the attack homing property to False, so the attack will miss if you move. And the attack type should not be splash

about the air unit trigger....

make the air unit invulnerable. or..
use an ability to change from one unit type to another, like druid of the talon.
The storm crow's [targeted as] property is set to air. so ground units cannot attack him :8
ask again if u can't do that.

c ya

I don't really know what type of game it is...
But you could always user a carrion swarm based attack, without the ability to hit air units, but then they wouldn't home in on you.