You don't need a lot of rocks. But you can help yourself by making SMB spawning structures. Very easy to make and some good examples in the archives. Just a few rocks will do fine.

This recent post talks about the myths that SMB can't do well in ponds or can't reproduce etc. There are many of us eager to dispel that myth and get more pond owners enjoying SMB. It is true that SMB and LMB do not do well together in a small pond so it is very helpful to do one or the other.

See this thread:

https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=554467#Post554467