Kryptonite U lock package that included the thick wheel. Look up on youtube how to properly lock up a bike with u-lock. Through frame and back wheel to a slide object (u-lock) and thick cable through tire/fork and into the u-lock to lock it up.

Nothing will be completely safe, but this will deter lazy criminals.

Best security? Park next to a nicer bike lol. Even better if the bike isn't locked as good as yours is...