Short Answer:
I just placed it in the center of he depression that the funnel forms, and tried to make sure the outer rim of the strainer was flush against the funnel all the way around.
I have 6 of these installed at various locations and in what are Rainwise or Rainwise-supplied funnels, along with a couple of Davis and a Peet Brothers, and no problems whatsoever with wind or other disruption. Being metal, they have some weight, and they are lower down into the funnel, and it would have to be one mighty wind to dislodge them in any way.
Never had a bird try to make off with one, either, but I haven't got many crows around where my wx stuff is, and they'd be the only culprits here.
I haven't ever had the concern that it might move or fall out. It is metal and doesn't float, so even when the pollen and chaff from the various trees do collect it does have to be pulled and cleaned, and the worst for plugging up the original round little plastic screen that fits into the depression of the funnel is when it is very dusty, there are small brief showers that wash some atmospheric junk which is very fine into the already present pollen and that can settle in the area below the original round plastic screen, but much less often than when the cotter key is in there making the orifice much smaller.
Unlike Randy, I've not had too much of a problem with this being a porta-potty for birds, but I can see how it might be attractive to them sitting on the edge and then reducing take off weight just before they fly off.
These help a lot in my heavily treed area and in the spring for six weeks when the blacktop driveway is greenish yellow with oak tree pollen and such onslaught, along with maple tree helicopters that collect and some long stringy flower parts from the oaks, I think, it cuts down a tremendous amount on the trips up to clean the collectors. The mesh is big enough that some stuff gets through, and I'd advise against trying to tack the stainless screen down with a few tiny buttons of silicon seal, since I take these out, clean, pop out the plastic disk, blow through the funnel and then reassemble once or three times a year. I guess a guy could put a BB sized spot a couple places around the screen and make sure, but I'm thinking that if wind is going to dislodge it, your location has a lot of other problems to fix after the storm beyond trying to find your screen.
If I can elaborate in any other way, let me know. I'm not sure how these would fare in really dusty areas like the SW with the haboobs and other major dust storms, with some rain afterwards which might make the dust into a sort of a cement.
I'm curious to hear from people in those areas who have a different filter problem. I'm guessing it is more dust than it is massive pollent and other aerial material.
Dale