You could also anchor it in with aquarium safe sealant (obviously before you put your fish in and let it sit for at least 24 hours). Maybe a few drops on the bottom and some on the side in the back (so you don't see it in the front)?
I am going to do this soon... i came home today to one of my divided tanks and couldn't find one of my fish... sure enough, he some how (NO idea how) made it to the other side and was wedged in the corner behind some grass looking guilty as heck. "Mom, i swear i didn't mean to!!!" Thankfully that side was empty so he didn't get in any fights (thank GOD he didn't decide to jump to the other side!!).