I would like to know this as well about the plecostamus, I have one in my aquarium that I am about to convert over to saltwater. I was planning on giving all of my large freshwater aquarium fish to the LFS, however if the plecostamus would thrive in the pond, that would be awesome!
The never ending watering hole is a added bonus, when I had the old pond with the stream, our dog used that all of the time, now he just uses the pool.
I wish I would have used a pool skimmer instead of the pos atlantic skimmer that I purchased. That is the one thing that I am considering re-doing.