When is the wedding, and what is the season? If it's going to be a colder season like winter, wearing opaque hose with a cocktail dress will solve the problem. And in that case, really dressy boots might work too - they have to be dressy though (a delicate heel, pointy toe, maybe suede). But I wouldn't wear the boots if it was hot; that would look odd to me.
If it's going to be hot, then go for a long gown - maxi dresses (while more casual than what you would wear to a wedding) are so in right now, I really don't think you will look out of place.
Actually if it was a daytime wedding in a casual locale - like the beach - a maxi dress might be just fine. If nighttime wedding in a formal locale, then you can probably safely pull out all the stops.
We need more details.