My leporacanthicus turned out to be plant eaters too. They would eat the amazon swords, but leave the crypts and anubias alone. So (1) try using crypts or anubias instead. (2) It seems that they like the base of the plant, so you may want to try protecting the base area. I use an old plastic lattice plant top, and clip some of the "cross hatching" from the bottom, flip the pot over and thread the plant leaves through the pot; I find that it also helps prevent digging and dislodging plants (I changed to another tank, and the light was not strong enough for amazon swords, but I used this method to protect an anubias planted in the gravel).
Never kept L128, so can't tell you what to feed it. Though I'm guessing wafers are find (Hikari, xtreme scraper, etc).