Sentinel buff on tree detectible by trigger?

I'm trying to make a trigger that does certain things upon units walking near trees that have a Sentinel on them spying the area.. however i am unsure of how to detect a buff on a destructible

any clue?

destructibles cant have buffs.. i guess.
Anyways, what you can do is to store the location of:
(Position of (Target destructible of ability being cast))
and then link the loc to a destructible which is in an array.
You can then check this array every x second.

Or, you can place a dummy unit at the destrs loc and then use the 'unit gets in range of' event.

Sentinel doesn't use a buff, it uses an effect. Whats the differance? Buffs are attatched to units, while effects are not.

use CS check for trees BUT use sentinel as control spell, order boolean will return false if sentinel uncastable but before you have to check for tree, cos any non tree will force to return null