Research chains a little before buying one. Some are hardened and some big ones that are not can be cut by a huge bolt cutter. The large Kryptonite chains are pretty strong. Keep the chain and the lock high and wrapped so one can not get a link on the ground. If a link can be put on the ground a huge bolt cutter and all one's body weight pushing the bolt cutter handle down against the ground can cut many chains.
Nice bike, did it get damaged?