Need help on the ruling of certain cards in yugioh!!!!!!?

Ok, so my friend and i duel a lot and he made this deck that uses spells, traps, and monsters to banish cards and bring them back. He also uses a lot of defensive monsters and he sets cards a lot. I want to side deck a few Imperial Iron Wall trap cards and some Dark mirror force trap cards for when I play him. Im just not sure If i can use both of these cards at the same time.

Imperial Iron Wall reads:

"Cards cannot be removed from play."

Dark Mirror Force reads:

"When an opponent's monster declares and attack: Banish all Defense Position monsters your opponent controls."

Now If I have Imperial Iron Wall on the field and its active and then I use Dark Mirror Force when his monster attacks, Instead of his monsters being banished, do they get sent to the graveyard? Or could I not activate Dark Mirror Force because it says his monsters get banished and Imperial Iron Wall prevents that?

Thanks for anyone who has the answer. Im just really tired of his banishing and defense monster shenanigans. lol he makes me rage....Show more

I dont completely understand what Nebul is saying. Do you mean i can chain them together? or that i can activate dark mirror force while imperial wall is already in play even though it says they will be banished? will they be sent to the graveyard instead of being banished?...Show more