oh, one other thing that may help. you may not have the room in a NC, but I was able to have a small, isolated pile of rocks for my nem - it was surrounded by sand and the rocks did not touch any of my rocks in the rest of my tank. this helps (but may not completely disuade) the nem from moving to the rest of the rocks. BTA's aren't too keen crossing sandy areas. Long Tentacles are definitely different - they love the sand. I would look for 3 things in an area for a BTA to be happy - good to high lighting, lower flow, and nooks / crannies where the foot of the nem can get into and anchor and be protected. (some people have successfully used short 1 - 1 1/2 inch pieces of 1" of or so pvc to create a nice home to place the foot. didn't work so well for me on one of my forays when my rose bta split...)