2) What can the enemy do to counter the embargo?
2: Nothing that I can think of at the moment. Pretty much the only way to prevent Barricade is to run a deck without permanents and have sufficient PC or EA in deck.
Wait a min.
Permanent control?
I'm speechless on how permanent control can interfere
spells.
... but, wait, Enchant Artifact?
Are you implying that you can sacrifice
your opponent's permanent to embargo them!?

This is going to be OP.
However, if you meant that the EA is used to protect
the opponent's permanent so that they can't sacrifice it, it's a whole new chapter.