I have never ever seen some1 come 2 my island when it is locked, from another island, and I am assuming this is a very rare issue, and does not need 2 be added No Support.
not if the island's locked. I've attempted /tpahere someone on a locked island not belonging to me and It went through but when the request was accepted it didn't work and sent the /tpaccept player a message about how players can't be teleported by someone on the island other than coop members of the island. tried it the other way as well.
You know how you cannot walk into the area of mob arena with the leaderboards, well do the same thing around ur island
No support, sorry. For two simple reasons, first of all, as stated above, it generates tons of unnecessary lag. And also, people will always find ways to get into your island. I've come up with 2 ways to bypass barriers after reading this suggestion once. People who fly onto locked islands often get guest banned, or reported to staff.
