The ballpoint pen trick is no longer true.
The vulnerable locks had tubular cylinders and they were phased out 5 years ago. The cylinder and key looked liked this , if you have one, get rid of it.
Kryptonite, the most popular u-lock, replaced all tubular cylinder locks for free. I traded in a 10-year old lock, they paid postage both ways.
Here’s a good guide to bike locks:
http://www.missinglink.org/Pages/bike_locking