I use the dividers from pet smart, forget what brand they are but I think Top fin? They work really well, just make sure you have substrate in the bottom so they can't slip easily.
Also, you can make your own, which makes it a bit harder for males to see each other, but they can be a bit more flimsy. Google "DIY aquarium divider" to find out how. I've made them before and they are okay, but the store bought ones, even though they are easier to see through do a better job for me.
Also, your males may be a little stressed when first moved into their new condos, being able to see their neighbors constantly and all, but after a few days they'll all calm down. All my males live within constant sight of each other without any issues. I've only ever had a couple slip through dividers and they were the crappy ones aqueon makes for their mini bows, no one has ever been seriously injured, just a missing piece of a fin when it did happen because they were caught in time. Good luck!