I had this come up at my job the other day. A customer insisted that she had never had problems with the common plecos she had in the pond with her koi. I tried to explain the potential threat that plecos pose to goldfish in general and she just wouldn't have it. Now I know that fancies are an absolute no-no with plecos. I also feel that plecos in a tank with common or comets is a no-no. But what about plecos in a pond with koi? And I guess for that matter plecos in a pond with commons/comets?

I once had a huge common plec in my koi pond back in Indonesia, and they got along peacefully.
I think the kois are much too large & too fast for the common plec. I also think large comets and commons are also ok with common plec.

Yep, Riz is right - there isn't much a pleco can do if a koi is about 100 times faster than he is...
A local koi dealer keeps plecos with koi on a regular basis, and the plecos aren't small either, about 10 inches long. Never had any troubles with them....

Alright, thanks so much for the quick advice, guys. It's good to know that the plecos and the koi will do fine together and for that matter the commons/comets too. I'm glad I finally got that issue resolved.

Yeah, all the pleco ever gonna see from the koi is their tail...