Don't want players abusing the /pvp command every time they are close to someone?
Use PvPManager signs! Write [PvPManager] or [pvpmanager] on the first line of a sign and then players can click that sign to toggle PvP.
Then to make sure they are forced to use signs set the "Disable Toggle Command" option in the config to true, so players can't use /pvp anymore.
You can also write whatever you want on the other lines of the sign, it doesn't affect how the sign works. If you only write in the first line then the other lines will get filled with the default PvPManager message.
(Will add pictures of a PvPManager sign soon)