Stop bid-blocking, revert to 1 day guild timer. Problem solved. Guilds found bid blocking aren't eligible for sieges for 1 month. (2 additional cycles). You either show up and actually siege, or u stop blocking for those alt guilds. If that portion seems too difficult, make it where only opposing faction guilds can siege a zone. This will also basically stop most bid blocking as there aren't many cross-faction alliances to help bid-block.