Not much you can do with fabric panniers given that lots of folks carry pocket knives (and pocket multi-tools can easily take thin cabling), but if you have a decent bicycle I figure it's still worthy of using a halfway decent bicycle lock requiring at least larger/heavier/louder tools, like 30" bolt cutters or better. Pocket-sized cable cutters, which can still take half the bikes out there, just seem too easy to carry, conceal and discretely use. Also, just being a bit more time consuming than the equivalent bike next to you can often do the trick.