"so, the more pillars/pends you have, the less chance it breaks something important? yes?"
depends on what you mean by that, it should count them by stack, not so much it can choose to target pillar #1 through pillar #10 in the same stack. but if you have several stacks of pillars/pends, yes, that would lessen the chance of something else being destroyed
"intended to trigger on sundial"?
could go either way, i was leaning towards "no" because it stops creatures from attacking in the first place, rather than causing attacks to attempted but be unsuccessful.