Twin Towers

I think it may be wise to construct twin towers at each entrance to Sparrow Lands.  Each would be small, with a gate attached.  This way, a guard could see what approached.  Also this could provide cover to guard.

This would help to "discourage" those who would attack Sparrow Lands.  Also perhaps the guards would be able to stop or at least slow down an attack from an invading force.  That would give the Sparrow enough time to rally a force to counter the force.  Perhaps even a drawbridge.

Also perhaps the Sparrow could send a trade delegation once a year to Nagai Aruki with art from the Sparrow clan.  This could provide money to build the defenses.  Though I think it might be better to build as funds allow rather then going into debt.

Perhaps the ronin who hold Daidoji Yukan-se would like to join the Sparrow clan.  While not as strong as the Crane, the Sparrow do share a common heritage.  They haven't been able to gain entry into the Crane clan anyway.