Hi Grant,
I'm also fairly new to Coaching. In fact, I've just passed my FA Level 1 and am still looking to get involved with a team. Any simple attack vs. defence games will all help in understanding and developing the players defensive play. Try setting up 3 to 6 (depending on numbers) small pitches alongside each other, and play 1 vs 1 games. Then progress to 2 vs 2 and then onto 3 vs 3 games, keeping all the goals in. This should also develop defending as a team.
I have also been checking out plenty of sites:
1-2-3 defending
TopLeague Animated Football Coaching and Training Exercises
Hope you can find what you're looking for.
Regards,
Lar.