Enhancing defense is very hard, nearly impossible. Its all about offense.
As a former alliance leader with great and crazy wars i have some ideas for you:
A good start would be to find a solution for cleaning strikes. A typical problem often is that nobody wants to “clean” an opponent because he says “my teams are too strong for that”.
One way could be to force your members to clean after he missed an attempt.
Another COULD be to take some of your weaker players and let them use all war flags only to clean enemies and not attack full opponents.
Those players should be very active players, AND it should be mentionned very often that they play a very very important role in wars, because the help the “strong players” to strike with full force on full opponents.
Third thing would be to skip some hard defenses and use the respawn timers of opponents correctly. It would take too long to explain every detail here.
4th tip: leaders should keep an eye on players that regulary have trouble reaching good scores in war. It takes a lot of experience, especially with the new field aids.
I personally struggle hard on the cleaning field aid, it some kind of kills my playstyle.
Using one ore more of my tips, can improve your war outcomes.