I also use manual with auto ISO - and when in AP I have the wheel on the back set for Exposure Compensation, but I've not noticed a real problem with knocking the wheel - it happens occasionally, most often when carrying the camera when generally walking about - and as I am in the habit of checking settings when starting to take a series of shots, it's not been a real concern.
On my old A900, which has 'traditional' front / rear dials I find I get a similar frequency of changed settings from accidental dial changes, so it's not a new problem.