Tbh it's not just law lecturers that are keen on keeping their lectures to themselves: some of my philosophy lecturers during honours were fiercely protective of lecture material (to the point of not issuing any) because they were currently doing research in that area.
Rule of thumb: Ask if you could sit a dictaphone near the front of the lecture theatre or on their lectern (the wee desk they stand behind whist giving lectures) but in general that sort of thing is only for kids that have dyslexia or some other learning impediment, so don't rely on your being allowed this luxury.