The wonderful weather here might erode a turf wall, but you could also put in hedging at the same time. Quite a lot of dry stone walls from the quarries are popular as well.
If you could put a sheep fence in ie wooden poles with animal wire and then either hedge or willow would be nice.
A lot of the farmers are putting in drainage ditches now and they do fill up with water.
There is a free tree incentive at the moment for non garden areas, but you need to google that.