Things to block at least part of the divider would be pretty good for both sides. My 2 constantly guarded the divider for about a week or two flaring and blowing bubbles and stalking each other. Ludendorff's tail is almost completely grown back in, he was a tail biter before.
Since I'm waiting to get a plant light to grow my plants, my divider is pretty much open on both sides (so they can always see each other). I'll be growing out my plants and covering it though.
Whatever works for you :)
Caves are essential for privacy and a dark place for most bettas. Mine barely use theirs but I keep them anyway.