A drillship at anchor in Maine, doing a thruster change out, can get a safety zone. See http://edocket.access.gpo.gov/2010/pdf/2010-15006.pdf .
Why can’t an operating rig in the GOM get one to keep the fishing boats away? I’ve seen line and hooks caught on the riser, in the HiPAP’s, and ADCP. We even lost comms with the ADCP because of a hook in the wire.