Sir,
Regarding Lynn in Washington’s pointer to the YouTube video (as representative of a “secure” lock?), I know of, and have known of, for quite some time, two ‘other’ locks which fit, much better, the criteria of “round” and “disk”.
The first “round” [1] lock is manufactured by the American Lock Company. (Yes, that is its real name).
Many truck-delivery companies (in New York City, and surrounding vicinity) use this lock on the back doors of their vehicles, and anyone who, honestly, believes they can open this lock with a bolt-cutter is being dishonest with themselves. Picking is also rather difficult.
The second lock (“disk”) is manufactured by Abus, and is known as [the]”Discus” [2]. I owned my first one while in High School during the late 1970s, and it never failed me (amongst a dorm full of amateur-lock pickers, this was quite an achievement). As seen in the illustrations, it would be extremely-difficult, if not impossible, under ordinary conditions, to push a bolt-cutter in to cut the shackle of a Discus lock..
That’s all here. You have a very nice blog. – Manatee