We have killed three in our backyard recently (orange cty)but they were
all under flagstone piled up in our yard.

My sister had a dry-stacked, circular 'wall' of white quartz rocks
around her herb garden in a field years ago (again in orange cty), and
on a rainy misty day a guy knocked on her door. He was from one of the
universities around, and asked permission to look for black widows in
her rock wall. He found 26!