How about Rf6. The point is to next move Rf1 and White must trade rooks or get off of the 1st rank. If he trades rook, we promote the h pawn and win. If he vacates the 1st rank, our two pieces should be able to escort the h pawn to promotion or force White to exchange the rook for the h pawn. Either result wins for us.
If he attacks our knight with his rook, h3 protects the knight while advancing the h pawn. If he then moves to h1, ..Nf4 protects the h pawn until the rook on the f file can come to the rescue.
If White opts to snatch our a pawn, we promote the h-pawn before he can promote his a pawn which will be blocked for a move by the knight.