As I understand it - if my neighbours sheep keep coming into my field I can catch them and pen them, feed and water them, which I have to do, but I then bill my neighbour for the work, time, feed, water. Not going to make you any friends but it might make them keep their sheep in! 
Interesting. we had numerous ingresses of sheep last year and neither of my two neighbours were interested in owning up (not when they could avail of free grazing). Only when my husband did a very good impression of a sheep dog and we rounded them up into our pens then told them both, did they own up. And surprise, surprise there were no more "ingresses" thereafter so they must have done something on their sides when they realised we weren't complete idiots.