I have had the Mosquito Magnet "liberty" model for a few years now and it has made the difference between our backyard being completely unusable at dusk and being able to sit out there all evening comfortably and enjoy our deck/yard without getting bitten to death. It is a bit pricey and you have to be absolutely DILIGENT about keeping up with the propane changes/line clearing/maintenance but if you do that your yard will be transformed. I am so spoiled now, and i know this sounds like a commercial but it's one of the things we 'splurged' on and it's been so worth it.

Mosquito coils, sold under several brand names, are very effective but would be defeated by the ceiling fans. If you are running the fans, that should be enough wind to keep the little vampires away, they're not strong flyers. The coils would be good to have on hand for times you don't want to run the fans, but not practical for those who might have breathing issues or around babies or folks who just don't like the smell of citronella. They're basically citronella incense so you get the citronella odor and the smoke.

There are also lemon/citronella scented Geraniums, if you can find them and have sun close enough to the seating for them to have an effect. Before you sit down, "ruffle" the leaves to release a ton of fragrance.

Keep foundation plantings to a minimum, and grass mowed as short as the type will allow. Put up a bat house.

I'm confused how your deck can be open yet be covered by fans? Do you just mean open on the sides?

I find that I'm not usually bothered during the daytime unless I step off of the porches and start walking around or standing in the shade. Once it gets near dusk, they go on the hunt and I light one of those coils if I'm not going in.