I think a turn limit could work, I'd put it at 5 though.
There are generally less things that get through this than wings, but this requires a 2 card combo to work. If it's temporary the combo isn't nearly as scary, as you'd need a PA for each shield, which would slow your deck down a lot.
And if you didn't PA it then they could break your shield.
Works for me. If I do add the turn limit, should the cost be adjusted? Currently, this is at 8|7. By comparison, Dimensional|Phase Shield is 6|5, and Wings is 4|3.
