please do not use wood in a pond!  keep in mind that what we live in is a very big pond too.  and i am sure what some have done to you and me.  get a book on asian ponds. japan ponds i have seem to have the best way to treat the fish and keep them alive.  other than putting a fence around the pond i dont know anyway to keep the little ones out.  and at 10cm's of water one can still become one of the past people.