I use a cable tie as the 'arm'... you have to make sure that you use the type with no minimum size, as some are 'blank' for the last part so they wont close down tight enough for a barrel.
I can then slide it off or rotate it to suit.
Mine's folded over to provide a bit more ridigity, and gaffer taped.
Rich found some really good stuff in his missus's shop, which is like a nylon decoration edge... so unless it's really hammering it, it doesn't absorb much water (so doesn't get heavy), it doesn't have memory, and it doesn't wobble.
I also have a little bit of black string which I use for those stupidly light breezes at places like bisley, that won't move a blade of grass but will move a kill.
The cable tie enables me to position the windy so that i can see it with my left eye, and it superimposes itself onto my right eye's view through the scope.
So, you want something that's light, but doesn't wobble or swing, doesn't flutter, and doesn't hold water.
I shoot a lot off my windy, but i'm starting to learn that you need to pay attention to more out there... when you have breeze from behind, it can get pulled into the vortex your body creates and gives you a false reading. It also took me 3-4 visits to my home range to see the same thing happen around a tree, which meant i constantly went the wrong side of the same target every time.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep