trigger quesion..

When computer's guard tower is destroyed,
build new one at the same position
if there is no enemy near by.

... Is this too hard to be answered?

It's not that its hard, its just kinda a long trigger, to check if there is anyone nearby is fairly complicated, you can easily create a new tower over place of the old, but if you want a unit to actually build it you could run into more complications.

I want peasant to build new one...
and I don't know anyone who knows how to do this,
so I am asking here... T^T