100% safe system is also a useless one. Hard to carry too thick of a chain. 12mm chain core hardened should make most bolt cutters useless, or take some really long levers - over 1m. With enough time, tools and determination, any bike will get stolen, it is usually enough to make your bike less expensive and better secured than the next.
The joys of the humble fzs600- not worth nicking to sell on so not in the sight of professionals, only worth nicking by teenage joyriders, so any chain/ disc lock combination should be a suitable deterrent!