Karen Walsh: Teens are trespassing on our land - what can we do?

I generally don’t mind when some people accidentally trespass onto our land. However, recently teenagers are coming into an old derelict cottage on the land and drinking, writes this week's letter writer.

Dear Karen, 

Our family farm is located in a very scenic part of Ireland, and we have had incidences of people trespassing on our land, causing problems.