Duga is tricky and take some time to prepare and execute(depends on how much gear you are willing to risk confiscated
)
It was fairly easy to pull off till just a few months ago. Even few tour operators, that take people (officially) into the zone, allowed their clients to climb duga. They just looked the other way ;) But last year there was a fatal accident... a dude from Belarus died there (non jumper). So this winter, the bottom parts of ladders of duga have been cut down (it's not super difficult to climb up without the first ladder though - just bring a climbing harness and a bit of rope for safety), and I'm sure the security now pays more attention of what's going on around the object.