I would never intentionally build over someone’s region. The amount of time it would take to come down to the surface and check every block would triple the length of my project. If i build over the edge of your region and it actually effects you please tell me and i will do something about it. For those of who who wish to protect your regions extra carefully redraw your regions but use the command

//expand [direction]

such as //expand 256 u
that will expand your region upwards 256 blocks. Then i will be able to know if i cross into your region.
Please do not claim a region near me for no reason.