I always use several locks - bolt, cable.....even a dummy lock to make it look like it's another lock....anything to deter thieves. And they will require more tools - hammer, cutters......
If possible lock it where you can keep it in sight while you're doing whatever you're doing. If you stop at a restaurant - sit by the window where you can keep it in view.
You sort of have to treat your bike like a beloved pet - tie it up to a post but don't leave it for too long.
My bike feels like an extension of my body so ....when my mountain bike was stolen a few years ago...I was devastated. It took several months to get my balance back.
The thief was a young gun named Jason....on the Queensway @ a gov office.....
In the office I'd vaguely noticed a young guy arguing loudly with the receptionist - he was irate....She called him Jason.....when I went out to get my bike - it was gone...the landscapers said they'd given a hammer to the guy....he gave them a story about being in an argument with his girlfriend and needed to take her bike....they fell for it like accomplices....also the police had surveillance cameras (but were fuzzy)....a year later I got a call from the detective ....they found my bike thief - Jason.
I received a cheque in the mail from the Solicitor General's office - of only partial cost of bike (he'd had to make payments). But it was something....I know this never happens.....nobody every finds a bike thief, right?
But in this case...there were many witnesses, connecting of the dots.....the thief stole it under the nose of too many people and got caught.
good luck to all.