I would suggest that in future you hook them on a milk float or a paper boy's bike for an urban fox, and on the keeper's quad or farm pickup for a country fox. That way the fox would build up a repetitive pattern of behaviour over the same area and seriously skew the results.
Either that or ask him under what legislation, and in what court on this fine island, would he sue you for carrying out a lawful and legitimate method of vermin control. As has been said above, "it's part of what happens to foxes"