I recently went to a jam where a friend ruefully showed me the $500 repair to their nice Martin. “You might want to invest in strap locks”, they opined.
So I purchased a packet of “Fender Strap Blocks” (aka fat rubber washers)
and installed them on my daily instrument, a new Yamaha.
They were too fat to work on the endpin of my mothballed/inherited Gibson L7.
Instead I bought a, slimmer, D’Addario “Dual-Lock Strap Lock” and clipped it onto the endpin.
Turns out: not a good idea
Yesterday I, belatedly, dropped off the new Yamaha to be setup by a luthier, and pulled out the Gibson to practice on until the Yamaha returned.
The strap lock totally secured strap to the endpin (good)
It also secured it so tightly that it twisted the endpin out when I put the strap over my head (not good)
(Turns out, the endpin was was held in only by friction with a thin sheath of rubber into a tapered hole)
This is the exact opposite of my intention putting the strap lock on!

QUESTION: What is a good/secure way to attach strap to said guitar?
The low boogie, ugly, temporary, but oh-so-secure, way I’m contemplating is to insert into the endpin hole a toggle on a loop of sturdy nylon cording.
Instead of an endpin there’ll be an endloop.
When the actual proper recourse is possible, push the toggle into the body of the guitar, and fish it out through an F hole.
Advice?
“Don’t practice for a week, work on music theory instead”,
to
“Give me the guitar, then you’ll no longer have a problem on your hands”
to
“Take it to the best luthier you can afford and follow their advice”
Thanks,
Bruce