Make sure to loop a lock through the frame and both wheels. I use an ABUS frame lock on my rear wheel (never has to be removed) and a kryptonite chain lock for the front wheels and frame.
If you want to get really secure, replace fasteners with tamper resistant versions.
Nothing is ever theft proof, but there’s lots of ways to make your bike very theft resistant.
I went to a Hotel Furniture liquidator for some new furniture. Saw a good looking office chair and they only wanted $20 for it.
Brought that bad boy home and only then did I find out that they had sold me a new Herman Miller Aeron for only $20. Completely insane.