You'd need a full blown X-ray to catch implants. I don't think technical countermeasures are the solution; even this is technically and logistically feasible highest levels of play, it wouldn't be something you could practically apply to the mid/low levels of play.

Inexpensive technical countermeasures like the metal detecting wands are reasonable enough, but probably not enough to stop the reputational harm that cheating scandals do to the entire sport.

They often have that. But if you have an accomplice placed with the spectators that person could just discreetly signal stuff. Like scratching the nose or so. At least for the WC matches they also often sat behind one-way glass.