...Add a condition to your spawning trigger (If/Then/Else work the best) Just make the condition boolean checking if a unit is alive, the unit should be the barrack/castle or whatever. So it would look like this:
Event: Every 30 seconds of the game
Conditions: None
Actions: If/Then/Else-
If (Boolean - (Barrack 01) is alive equal to True)
Then (Unit - Create 03 Footmen at (Position of (Rally-point of Barrack 01) Facing default building degrees)
Else (Do Nothing)
Something like that should work, there is no movement triggers in this piece so you will need a different one for that. You can just put multiple If/Then/Else of this type in the same action catagory, just make sure one isnt inside the other and it should be OK.[/code]