So the ruins are to be gathered while under construction? Or only when fully constructed? And they should decay while under construction, or only once fully constructed?
For just removing the spawning while that thing is a foundation is to modify the special/filter/formation template to disable SpawnEntityOnDeath.
Add the following to the <Health> tag: <SpawnEntityOnDeath disable=""/>. That way no foundation (so this is not limited to this specific template, but to all) will spawn an entity on death. If that is what you want I cannot tell.
Auras stack if you make them stackable.