Good question.
We will be using chess.com who is very good with detecting bots.
Furthermore I will not allow games longer than 10mins a side. It is very hard to cheat when you have a tight time limit.
Chess.com only detects bots some time after the game ends though - int's not instantaneous. Besides, bots like Stockfish can easily play a 10-minute game. Not very hard when you're feeding the information into stockfish by mirroring the other player's moves on another board.
The asymmetrical nature of chess inevitably favors the high ELO players to get all the rewards though, it's not a luck-based game.