I did a TTD session, but went in the pool. It dried over night, which surprised me. I haven't taken it to the cleaners yet ...afraid of the bill.
I agree that you should direct the novice TTD photographers to examples of what you are expecting or would like. But, really I think once they realize what you want to do they'll have a lot of great suggestions and ideas. I know my photog, Jonathan Thrasher, had a lot of great ideas.....and, I don't think he's done a lot of TTD sessions.
If your dress is silk, I would definitely get a second dress. ..my dress was polyester.