There is an article in the Oct 2006 issue of Cichlid News Magazine by Radek Bednarczuk, about his experiences successfully spawning Acarichthys heckelli, that I consider well worth reading
There is also experience in the book South American Earth eaters that suggest long pieces of pipe to emulate the tunnels Acararichthys use in nature.
I thought I was on the verge of having mine spawn, but in Radeks article he talks about needing nothing smaller than 220+gallons, or the aggression becomes intolerable, which mirror my experience in trying to use a 150 gal tank, and ending up with a lone individual