I've tried the Jardini idea and it hasn't worked out too good...The 12" Jardini doesn't bother my big clown, if anything the clown pushes the jardini around, but the jardini is so fast he steals the food meant for my big clown knife..
My royal knife is another story, he's much smaller than my clown, and the jardini beats him up ( he's got several bite marks on him ) The Royal tends to hang by my Clown for protection cause the Jar won't mess with the big clown. Jars are a little too aggressive in my opinion, that's why I'm getting rid of mine. I've never kept bichirs, but from what I hear and read on this site they would be a better choice. I have successfully kept my clown knife with a South American red-finned pike cichlid, they actually got along great, and the pike was close to a foot and never a problem.
Hope that helps
Jude