Just place an object, or unit on the map and call it name it pos1
just place this in a triggers On Act box
bomb = "GrenadeBase" createVehicle [(getPos pos1 select 0),( getPos pos1 select 1),0.5]
set your trigger up to anybody present and place it over the object or unit.
If you want you can attach a trigger to a unit.
You name a trigger trig1 then in the init box of a unit named pos1
trig1 attachto [pos1,[0,0,0]]
now if the unit moves around the map the trigger moves with it.
You will need to set the trigger to the opposite side or it will go off immediately.