What a great classic variant I've only recently discovered! This description mentions that you can use only one board. I agree and think it's easier visually. After each piece is moved, you could just mark it with some sort of large poker chip underneath (or clip something onto the top) and vice versa - when a marked piece is moved it loses the marker.
Then, the players could simply have an understanding that marked pieces and unmarked pieces are not in each others' way and cannot capture each other. So a game could go like this:
1. d4 Nf6
(now the white pawn and black knight are both marked)
2. Qd6 now possible for White because White knows the unmarked Queen can go "through" his/her marked pawn. Then the Queen becomes marked at d6, threatening the marked Black knight. The Black knight then moves to e4 and loses its marker.
What a great classic variant I've only recently discovered! This description mentions that you can use only one board. I agree and think it's easier visually. After each piece is moved, you could just mark it with some sort of large poker chip underneath (or clip something onto the top) and vice versa - when a marked piece is moved it loses the marker.
Then, the players could simply have an understanding that marked pieces and unmarked pieces are not in each others' way and cannot capture each other. So a game could go like this:
1. d4 Nf6
(now the white pawn and black knight are both marked)
2. Qd6 now possible for White because White knows the unmarked Queen can go "through" his/her marked pawn. Then the Queen becomes marked at d6, threatening the marked Black knight. The Black knight then moves to e4 and loses its marker.