Cat Guard for Top Computer Fan

I can't find a commercial product to do this, and found several other folks looking for it but no models. This just sits over the top of my computer, over the fan. The cat no longer lays over that warm fan outlet, with the gentle breeze distributing its farts far and wide. I also have a lamp on the top of the computer so there is no place for the cat to perch and push this off. I was thinking I would have to secure it with double sided tape but it's been there for a year without being disturbed. YMMV but yes, this is hostile architecture for cats.