Jörg Knappen wrote on Mon, Sep 5, 2011 01:43 PM UTC:
I suggest that you take a chess board, two kings and some piece representing the rhino (a knight works well for me) and try it out.
I must admit, that I didn't analyse the specific position nnz gave here, the placement of the supporting King is a bit awkward here. Both of your proposals to repair the situation work out fine.
For similar pieces: A gnu and a king can drive the king to the edge, but cannot give mate; the same holds for the quintessence (of quintessential chess).