The best way to keep your BTA from wandering all over your tank and killing the SPS in its path (I've had it happen even after months of the anemone staying in one place) is to create a little rock "bommie" that doesn't touch any other rocks or the sides of your tank (by several inches). BTAs don't like to walk over sand, so the only way for them to get off the island is to let go and float.
Keep in mind that this will only work if you've got the right conditions on the bommie - good light, flow, crevices for its foot, and do on. It's also hard to do in an established tank.