U Lock that reaches thru the rear stays and onto the thing you lock the bike to.. Plus a hardened security chain

you have to secure your bike To something and be able to keep both wheels . at least..

instead of a U lock I got an Abus Bordo Granit . it is a folding link lock so much easier to carry than a U Lock ..

ABUS Folding Lock 6500/85 black (55160)
it is their most secure heavy model, they make others that are lighter ..