Chain lock AXA Cherto City 1000 x 8 mm
Long and thick, that's what she said.
By the rule of thumb, if someone wants to steal your bike, they will anyway. But you can certainly make it harder for them by locking it with a thick chain. This one is long enough to connect your bike inseparably with a stand, pole or another bike.
Works perfect either alone or in combination with basic frame security.
Cherto City is expected to last, therefore it comes with 3 keys so you can either share the lock or lose more keys.