First of all, the word you mean is menstruating. Women bleed when they menstruate; they never bleed when tbey ovulate.
I suggest you don't have employees say this question directly, but print a short statement that sharks are attracted to the scent of even a small amount of blood, so women on their menstrual period or anyone with an unhealed cut should not go in the water. At one point in the rental process (before the customer has paid) the employee should show the customer this printed statement, tell them to read it, and then give a signiture saying they have read it. The employee must do more than ask a distracted customer to "sign here." People sign things they haven't read all the time. The customer must be told to read the statement, and the employee must stop what else they are doing to watch them read it. In this way you call the customer's attention to the importance of reading the statement.
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