I like catch in focus, I have aluminium tape on the back of a few lenses like my Helios and it works perfectly.
However, my Takumar 135mm is a slim lens that doesn't cover the camera contacts
On the base of the lens there is a recess, arrowed 'A' - the face arrowed 'B' is where the adaptor fits.
This recess is on a non rotating part of the lens.
So I made an aluminium disc 1.2mm thick, 52mm inside dia' and 67mm outside dia'. I didn't make the disc to tight tolerances, it was a compass and file job, and I smoothed it off with wet and dry.
The ring fits the recess, and when on the camera shorts out, and protects to a degree, the contacts.
It's not so tight that it fouls anything, doesn't make the mount tight or alter infinity focus because the lens still mounts on the proper face.
If you want catch in focus on a lens that is slim then look to see if there's a recess, or if you want to do close work where infinity focus isn't going to be used you could make a ring to trap under the adaptor, for that you could use something very thin like a drink can which can be cut with scissors.