released a new tool on our forums
which ensures your missions can only be played by Combined Operations players.
Quote Deadfast :
Dependency Enforcer (or just The Enforcer for short) allows you to add a Combined Operations dependency to your mission. This eliminates the current problem of Arrowhead-only players being able to connect to missions built with ARMA 2 and ARMA 2: Operation Arrowhead (Combined Operations) content before finally receiving an error message. With missions patched by The Enforcer, they will error out with missing addons (Chernarus or Takistan), before making it to the lobby.
It also allows advanced users to view in detail which addon classes the mission requires and in which content category they belong (ARMA 2, Operation Arrowhead, the content shared between the two games and community content).