Need help with trigger

Need help with this trigger-
How do you set it up so that my hero will have a unit following him once he summons it? The move is Called: Call of the Storm, it calls a unit with the base spell being feral spirit. I need that unit on any command of the Hero to follow him. Please help.

Please could someone answer me? I need this in my map soon. Anyone?

Well i think And pls hence me on think. u do
event: last summoned unit
condition: summoned unit = to wolf or what ever it is belongs to owner of unit (hero or unit)
Action: unit- issue order to unit to follow (unit)


I think im a tad new to this since early this year
if it is right let me know because im still learning good luck

Event(Generic Unit event) - finishes casting a spell
Condition(ablility comparison) - ability being cast equal to <your spell>
Actions(Issue order targeting a point) - Order (UnitGroup(pick every unit in units of type <your unit>)) and order (picked unit) to (follow) (castingUnit)

Last created unit will not do anything if it is trying to respond to a skill summon. Last created unit only selects the last unit made with the trigger create unit.
Summoned unit would work, except that if this is finishes casting an ability, there might be a time lag between when the unit is summoned and when the trigger runs. If is is begins casting, the summoned unit will not exist yet. If there is a time lag between the summon and the trigger, another unit might get selected instead.

I suggest:
Event:
Unit finishes casting ability
Condition:
Ability comparison ("ability)
Actions:
Pick every unit of type("whatever the summoned unit is"){
order picked unit to follow casting unit
}

yes mr. obliteration is rigth but u should add a wait period in there just for good measure. it couldn't hurt but it could help.

I suppose a wait couldn't hurt, but there isn't really any need