Try an oxford docking station with longer resin anchor bolts into the ground, the lock is an integral part of mounting bracket and it would take some serious cutting to get through it, its also got a self adjusting lock (have no idea of how to describe it) so basically if you lose the first key, you use the second and it makes the first one useless, and so on for the third key...
I use an oxford nemesis chain whih was 200 and too thick to get any bolt croppers on. All the cheaper chains are thinner and can be cropped.
Ive had this set up on my bikes in the city centre of leicester and never had any issues with it being nicked despite it being on the main road.