Another snail problem

Ive got a problem w/ some trumpet snails. Ive got a planted aquarium, and
they really kind of help the aquarium.. There are a lot of them but the
population isn't out of control or anything. I usually dont see any durring
the day, but they come out at night. The problem is that one of my fish
loves to eat them, but he cant digest them. I had to have surgery on the
fish to get them out of his gut!
So, I want to get rid of a lot of the snails. I dont want to use chemicals
that could hurt my fish or my plants. Everyone talks about using loaches to
control the population. The only problem is that i think my fish would eat
the loaches. Ive got an oscar, jack dempsey, severum, and convict living in
this aquarium. All of the fish (other than convict) are over 7" long, and
the oscar and dempsey have big mouthes.
There is plenty of cover in the tank.. Most of the bottom is covered in a
maze of plants. Do you think the loaches would look like food to my big
fish? Do you think the plants would provide enough cover for the loaches to
safely hide in? Does anyone know if its possible to get large loaches?
(few inches at lest)(all the local pet stores say they can only get babies).
Or, is there anything else I can get that loves to eat snails?

Thanks