Bergischer Lowe shank condoms
You know the one that gets loose after a few shaves and slide around, and that looks like cheap heat-shrink tubing instead of nice grippy ribbed rubber like the old Pumas? Yeah, that one... Turns out that it *is* cheap heat-shrink tubing.
I finally got tired of mine sliding around and squirted a good bit of oil under it to help prevent rust, then flamed it with a match and it shrank back down tight again. I'm curious how long it will stay tight, but it's a pretty simple procedure, and if it loosens up every few dozen shaves then that just gives me an opportunity to keep it good and oiled.