Raids that are 100% a single Guild are not as common as they used to be. In fact, I suspect that most raid forces these days are rarely comprised of characters that are 100% from the same Guild (with the exception of the top raiding guilds). Due this, raid members who are not part of the main Guild in the raid, may not have enough members to plant a Banner of any kind. With that in mind, how about a new Banner simply called RAID BANNER (that can be set by the Raid Leader)? Then add a SPLINTER FROM A RAID STANDARD to the guild hall vendor, that would allow you to use the Guild Hall Portal to get to the Raid Banner -- no matter what guild you are in or what Guild set the banner. So long as you are in a raid and a Raid Banner has been set for that raid... it works. Anyone who tries to use the Portal when the Portal is set to the Raid Banner, will get a message, "The teleport failed, as you are not part of a raid where a Raid Banner has been placed."