I use the sticky strips that come rolled up. They come in packages of 3 or 4 and have a loop at the end. I remove a lens from a saloon light, put the loop around one of the "legs" of the lens, and then push the lens back into place. It effectively hangs the strip in the center of the saloon.
It works great, and they are cheap to buy and easy to store -- we have some in the cabinet a few feet from me, but haven't used them yet this summer. If flies show up, I put one up for when we are off the boat, my wife doesn't like how they look, so I take them down at night. (Me, I like to count how many fliles are on it, to track our efforts.)
I cheat by putting a small bit of food on it. But flies like to rest on things, so they eventually "find" it anyway.
Been thinking about a way to have them go out of sight and be re-usable. Have some ideas, but none implemented yet.
(from the boat via long range wifi, somewhere in New England)
(may not have showered yet today)