Rowing is a great exercise to build strength and endurance. Years ago I read about single leg rowing in a magazine and I always used as a part of my training ever since. Single leg rowing is a great way to work on your technique but it is also great to challenge your legs one at a time. I usually use single leg rowing when hit plateaus in my rowing training. Single leg rowing is a great way to challange your rowing workouts and for spicing things up.
Check out video below for the demonstration of single leg rowing.