How to make a trigger in Starcraft that checks for units remaining at Location?

Is it possible for me to make a trigger that has a series of conditions which boil down to:

# of "unit" deaths at "Location"

OR

player ____ commands # of "unit" at "Location"

I've already tried "If Player X brings at most # 'unit' to 'Location'", and it doesn't really work- the trigger springs automatically, regardless of whether there are the set number of units at "Location" or if there are more.

Help, please?