To really scare the crap out of horses you need a Lama and pick a landing spot about 30 yards from the field boundary.
Then you can watch the spectacle of 3 horses tangled in barbed wire and the farmers wife getting badly cut trying to save them.
We were only saved from the business end of a 12 bore when it became apparent that the forestry commision had failed to notify the farmer that we were landing at this site.
They had previously agreed that this would happen in time for the horses to be moved.