87.(1,7)
Chess on an Infinite Plane - Huygens Option

Ok, I resign. I think you have a mate-in-2 (move guard, and put your rook on file -1). I wish I could challenge you again, but I'm in a few games already. I hope to play again sometime. Great work- you played an excellent game. Final board diagram below.

What about this one?
86...(-1,9)