To make my betta flare up, i just use a mirror. A handheld mirror IMO is a good choice in that it could be easily taken down or put back up. My betta flares at the mirror every time i put it up. Good excercise for him though leaving the mirror up their for around 5 minutes or so.
Hey SRC, two of my bettas are in the same tank, they can sorta see each other, but only like their shadows. Yes the tank is divided. Is that ok for them? I don't want them to start biting their tail.
I would say ig they haven't already then they probably aren't going to start now. Tail biters seem to be nervous fish...I'm fairly certain you'd know if you had a problem by now.