Your horse should enter the ditch on the short side. Have your horse walk through and step out on the other side. The obstacle’s challenge is the narrow space through which your horse has to walk. Practise walking through it, but also get your horse to stop in the ditch.
A second option is to use in-hand training to have your horse jump over the ditch. Let your horse have a good look first and don’t force it.
Difficulty level (1-4): 2