I love a silhouette and often like to do one at weddings. If you are lucky enough to have a stone arch then that really is the icing on the silhouette cake. Gateways are good but arches are better! This shot was taken at the wonderful Solton Manor wedding venue. The owner as built stonewalls and arches from a reclaimed church all of which provide amazing photographic backgrounds.
I use a remote flash on a stand normally set to around 1/8th power and 'hide' it behind the couple, This is obviously much easier if there are two of you but it is still quick and easy to do on your own. I have been using the cheap Yongnuo YN560-III & RF-603 for a couple of months for OCF work and really really can't fault them.