The ISF is considering an improvement to the anti-chasing rules written by GaryLShelton and me. It's now called Article 12 instead of Article 11 because the ISF is also going to add a new section earlier on in the official rules. There are two versions shown below, the RBP (repeated board position) version makes no changes at all to current game play but simply improves the clarity of the rule and gives it a solid logical foundation. The SMT (square moved to) version goes further and reduces the number of pointless chasing moves a player could make during a chase sequences than is currently allowed. For example, a typical double chase is blocked after 12 chasing moves by RPB, but is blocked after 6 chasing moves with SMT. If you are programming from scratch, and especially for the online game, I think the SMT version is the best way to go.
12. Repetition of Threatening Moves
To threaten is to move a piece to a square adjoining a square of an opposing piece.
To evade is to move a piece away from an opposing piece that has threatened it.
A chasing move is a move that threatens a piece which then evades it on the immediate next turn.
A chase sequence is a series of consecutive turns in which every move made by one of the players is a chasing move. The player making these moves is said to be chasing.
A chasing piece is a piece that has made at least one chasing move during a chase sequence. A chase sequence may involve one or more chasing pieces.
12.2 (Limits the chasing of one or more pieces that cannot be captured) (RBP Version)
A player who is chasing may not move a chasing piece to a square that creates a position on the board which has already taken place during the chase sequence, unless it is to a square the chasing piece came from on that player's immediately preceding turn and the Two Squares rule is not violated.
12.2 (Limits the chasing of one or more pieces that cannot be captured) (SMT Version)
A player who is chasing may not move a chasing piece to a square it already moved to during the chase sequence so that it threatens a piece that already evaded it during the sequence, unless it is to a square the chasing piece came from on that player's immediately preceding turn and the Two Squares rule is not violated.