Posted: 08/02/2014 at 14:33
Please, please do not plant blackthorn - The thorns are notorious for causing abscesses. We used to have terrible problems when the farmer trimmed his hedges, the thorns used to go up into the hoof - a blacksmith's nightmare and a vet's delight re expensive treatments!!
I too suggest a good gap between fence and hedge - Horses have long tongues as well as long necks and with the exception of holly, young leaves would be a delight!
I would suggest that you go to a tree nursery and get some really good well grown stock, so you stand a good chance of the hedge thickening quickly. Please don't be tempted to plant conifers - Colic and vet bills plus possible death if you don't know what you are putting in.