Oh Graham I have a feeling that there is something in this although it is quoted as an urban myth. We have had to move Jess's horse from where it was and you know where we live. The horse was on a field with good grass at the end of a drive and the farm is up for sale. When Mike and Jess went to feed the horse hay one night approximately first week in January they spotted a car in the driveway, when they turned up the car drove away, and returned twice having done a mile circle. I do not think they were lovers I think they were horse watchers. Our horse who is usually easy to box and to catch had been very nervous for about 3 days.
We padlock our gate now at night and when we go out - I would advise caution myself and please let us know what happens there is not enough communication going on about these issues and let's face it large horses are very interesting for the meat markets in Italy and further down in France - sorry to be brutal.
PS if it is just some stupid right of passage for youngsters to cut forelocks this would still be a concern as would your insurance cover you in the event of the horse trampling the offender?