Do we know if any searches were carried out in those areas? If he needed the toilet the logical thing may have been to climb the stile to go into the wood and he may have got lost but even then, he would have had to have taken ill whilst lost.They are all fenced off to stop the deer from getting in but all have access stiles to get over the deer fences.
If it's not that then I can't help but think there may be a more sinister side to all of this.