I have wrapped the fork in a paper napkin, tied it with ribbon and served it with the cake at more casual weddings. I've also placed it on the cake plate. I agree that by the time the cake is served, the dessert fork is long gone!
I have another outdoor wedding coming up and insisted that the wedding planner rent a canopy in additon to the dining tent. Her idea was to move everything into the dining tent should it rain. I absolutely hate that idea! The last time that happened, the beautifully set tables were trashed by the time dinner was served. We went through more silverware, napkins etc than necessary because of it. The staff had to basically set up the tables twice. We've had such lousy weather up here lately, that I can almost guarantee that this formal field wedding will be no exception.