Careful. Tilapia and some plecos are illegal in many states. Here in NY, ponds have different laws altogether from aquariums and you can only legally keep natives without a permit. For goldfish and koi the permit is easy to get and may even be free (I don't know), but it can get complicated. I don't know about other states' laws, but I would check before I installed a pond. Another bit of advice - small children drown quite easily in ponds, and if your neighbor chooses to let a three year old loose and the kid wanders into your backyard and drowns in your pool, you may be legally responsible. It is a good idea, therefore, to put the pond somewhere small children cannot access it easily.