Adamantine Sealing Chains

Using her chakra chains, Kushina can erect a barrier that is strong enough to prevent anyone or thing from neither entering nor leaving the perimeter defined by the chains. The barrier is very resilient, as Hiruzen stated that there was nothing anyone could do to interfere with what Minato and Kushina were doing after reaching its boundaries.

Fanon variations
Kodoku can enhance the chains with his wood release nature to make them grow and strenghthen them. They are so durable at this stage that it is considered to be Impossible to break.