Useful types: hardened security chain, integrated lock ,
Cable, but armored with steel sleeve sections over that cable,
and Abus Bordo granit 6500 , a folding steel link lock ...

and U locks ... have worked for me and others..

but most important .. Location .. don't live or leave bike,
in places with roving gangs of guys with power-tools that steal bikes,
in the blink of an eye ..







...