Do you know the old Scuba Diver's joke about getting away from a shark? Answer, you don't need to out swim the shark, you just need to out swim your buddy.

The same logic applies to bike security. You want a less attractive bike, that's locked better than others nearby. That will have the thief pass you for better pickin's.

At work, or downtown, where your bike will be locked for a while, then a U-lock secured to a fixed object like a tall signpost is best, and in many places necessary, sometimes along with a secondary lock for the front wheel. OTOH- short term parking at shops, especially smaller ones don't call for the same security, and the same U-lock slipped across the seat stays to immobilize the bike is more than adequate.

When I lived and rode everywhere in Manhattan, I left my lock in place on "my" signpost at work, and carried a lighter cable for short term use at stores. At work, it doubled as my front wheel lock. You might adopt a similar method if it makes sense for your situation.