“intrusive measures” would be things like having staff go round each tennis court and ask each player on the court to show their
membership card or guest payment receipt. It could be done, but would be intrusive to members’ experience. A possible future alternative would be courtside tap-in for all players or at least a system that records who the players are supposed to be (which we do not currently have).
But a lot of time, trouble and expense will be saved if members simply follow the rules.