Inner Moat
noun
The inside ditch is the inner ditch, or, if you make it awesome enough, the inner moat. If they get through the outer moat, we have the inner one, at least!
This word uses the kun'yomi readings. For 内 that's the reading you learned with the vocab, and for 堀 it's the same reading as always — just watch out for the rendaku.
私は彼を内堀に通すために道をあけた。
I stepped aside to let him pass through to the inner moat.