Kryptonite used to sell to people fairly thick metal posts with a 9-12" solid steel ball welded onto it for use for bike parking. Very simple, very elegant, once installed, but looked like a pain to install because of it being so top heavy. Apparently it didn't sell, as it looks like they are not being offered anymore.

Here is an idea for those Toronto rings... why not have them mounted so they spin/rotate somehow on the posts's axis? A bottom bracket is welded on the pole, the ring is placed on the pole where it can spin freely (like a vertical windmill), and a top bracked dropped on top of that and welded/brazed into place. This will make it harder for a would-be thief to get the required leverage with a 2x4, as the thief would have to push up/down to break the pole off, not sideways.