The adjective indefensible is commonly used to describe something that cannot be defended, but it applies to the defender, not to the attack itself. I'm wondering if there's a reasonably neutral word for "cannot be defended against". Something in the same spirit as foolproof, but less general and without the connotation of being proofed against fools.
For example,
I believe it to be bad policy for a game to have an [adjective] move.
whose meaning is identical to
I believe it to be bad policy for a game to have a move that cannot be defended against.
The term unavoidable comes to mind, but strongly implies that whatever is "unavoidable" must happen, whereas the adjective I'm looking for is conditional on an attack that may or may not happen. Unavoidable also doesn't imply defense. In the example above, "an unavoidable move" might just as easily refer to a move that can easily be defended against but that must be made at some point.
Any thoughts or suggestions?
Thanks in advance.