steve tried to do that too and in the beginning said he did not want to put guidelines on what people wore BUT i was afraid they would show up to the ceremony in their wet bathing suits ...
after talking to his mom, friends etc. they wanted a guideline and idea how to dress....everyone wants to be dressed appropriately for events.
maybe you can suggest it on your website instead of on an STD or invitation...
we had an FAQ section on our site and one of the questions was:
Wedding Attire
What should I wear to the wedding? We are having a relaxed, beach wedding weekend, so we are encouraging a "beach chic" look for the events. For the ceremony, men should wear a nice shirt and pants (Tommy Bahama look is good), suits and ties are ok but not required by any means. Women should wear dresses. Sandals are ok, but please no shorts and flip flops during the ceremony.