I have had my two male bettas in their own 1.75 gallon tanks for about 1 year and I have decided that I would give them more space and a better quality tank that is easier to clean.
For what I thought was going to be a simple "divide" and conquer mission has become a divide or die situation. My male bettas have never jumped before as I've had their tanks without a lid for over 1 year without incident. I started out with this:

Good clean and simple half divide where they were perfectly fine for 1 day, a flare here and there if they managed to see each other pass the divider.
And then came today:

I spruced up their halves with some black and white rocks with attached plants for beauty and cleaning functionality.
This is where I ran into the jumping. (I have no pictures obviously because I put them back as quick as I could before they can hurt each other)
Having no extra divider materials I had to go out and get some. This took about 1 hour where they were able to keep to themselves (thankfully).
And now the tricky part, I wanted to keep the Ying/Yang feel of the tank but I had to get it messy because the gravel was going to shift on me.

I pulled out the first divider (after placing my bettas in cups) and cut everything to size to create another divider. I then created this 3-way divide where I will be placing my clippings from my other tanks to retain water quality and to siphon water during water changes.
In the end everything is starting to work out but now my two boys, because they couldn't handle a single divide, will have to deal will a smaller swimming space but I will have peace of mind knowing they can't hurt each other.
My boys in their smaller but safe divide: