PVP Log plugin

Hello everyone, My server is PVP and so. And everyone is pvp logging. But they are not logging out. They are using commands to get out like /island. Yes, This is a skyblock server. And when they type /island it doesnt take seconds.

I need a good plugin to stop logging out while in combat. (Not alot of people log out but they use the /island command.)

I need it to be a bukkit plugin, or a .jar. If you got the plugin. Thanks, send the link or go on the server. sky-craft.us.to

Thanks and goodbye