There's nothing preventing them from making a run at the upper lefthand walk...
Also, when you build a 2 layer wall you need to be able to repair the front layer, otherwize there is really no point. I saw in one of the fortshowcase threads a 2 layer where every block interlocked with the one before it. That's probably the best 2 layer wall you can make. Every block is repairable, and any block that is destableized holds it's position until you can refreeze it (although they will probably just shoot it out while it's weak).
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I JUMPED THIS FAR
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