Each to their own Wyn. I used to insist until I realised that after the aggro stage, the offending shooter will simply borrow some glasses to shut you up then carry on with the rest of the shoot without them. Quite honestly, on ref's money I'm not willing any more to put up with avoidable grief. I'll mention the eye protection rule to them but I won't bar them if they want to risk their eyesight.
At Longridge on Easter Monday there were about 25 or 30 non registered folk out for a jolly day's shooting. Hardly any of them wore glasses and I don't think there would have been enough loaners in the office for all of them.
Perhaps it shouldn't be left totally to the ref, how about the shoot organisers mentioning it to the non registered entrants or even print it on the score cards.