.I have a Brompton and it never leaves my sight.If they don't let me in ,and to be honest that has never happened yet, then i go elsewhere.I never carry a lock.At present I go to the movies with it,shopping ,restaurants,libirary, dentist office,Costco,Lowes etc.That why I bought a folder.
If I had to go some place I had to leave it outside it would only be a place where I could see the bike at all times. I have armoured cable lock the kind has the cable inside a flexable armoured tube.It won't stop them from cutting the lock but it would give me ample time to get out side and get my hands around their throat.