If this person is a regular he should respect being reminded of appropriate "clothing optional" etiquette. Also, if he respects and appreciates the freedom we have at DCHS he should also respond to being reminded that it can easily be taken away. DeepCreekVolunteers.com has some stuff on clothing optional etiquette that is useful - basically that DCHS is a family friendly place and that being nude is not an overt invitation to sexual activity (or advances).

I would suggest reminding him yourself of the importance of maintaining this etiquette, or if you are uncomfortable doing this, ask someone else who goes regularly to talk quietly to him and remind him.

It actually wouldn't hurt to have this conversation generally among the naturists who are there, so even if it is not possible for others to identify the person in your absence, it still could be useful to have the conversation.