Flying units buying at taverns.

Ok, my problem is this. I created a tavern (custom, only slightly modified -sells custom heroes). And I don't want flying units to be able to purchase a hero.

I tried making a trigger. I used the following:
Event
Unit - A unit Begins casting an ability
Conditions
And - All (Conditions) are true
- Conditions
- (Unit-type of (Casting unit)) Equal to ****
- (Ability being cast) Equal to Select Unit
- ((Unit-type of (Targeted unit)) is A flying unit) Equal to True
Conditions
Unit - Order (Casting unit) to Stop

Where **** is the name of my tavern unit.

I also tried the following for the Event but they didn't work either.
Unit - A unit Begins channeling an ability
Unit - A unit Starts the effect of an ability

Any suggestions?

PS. I already tried searching the forum, but go no results for "flying buying" or "flying tavern" and I can't search for buy because the word is less then 4 letters. So if my question is already answered in another thread, just point me to that thread.

Place air pathing blockers around your tavern. This will allow ground units to approach it and not air. They are under doodads --> pathing blockers.

The problem with that is that I DO want flying units to be able to fly near the tavern to be able to see it.

make a new custom skill off select hero (might have to SLK edit) and make the target "ground". give that to the tavern instead of the regular select hero.

I tried editing "Select unit" but it didn't work.. but editing "select hero" might work... Thanx for the suggestion.

pshh... a few days without warcraft and i'm already losing my touch... i wonder what will happen in three weeks.