Forum:Lockdown

I have been told by a few people that you cant have 2 marading captains or 2 dupe frogs and then have you opponent not attack. They say that in that situation you choose one of them to attack. I have yet to find a ruling on this and they say it is a new rule. Is there or are they planing and such ruling stating that you cant have a lock down involving 2 of the same "cant attack" creatures?