I had trouble keeping smaller plants rooted until I fiddled around with my 'scape enough to ensure each of my plecos had a satisfactory (to them) hiding place. My male prefers a cave like affair-so it was a matter of elevating the back end of a slab of driftwood so he could dig underneath. For my female, it meant finding and tucking a vertical slab of wood in a corner--she prefers to perch vertically and needs open swim room to get in and out, where as the male is happiest if it's a tight squeeze to get in and out of his cave.
If they've got a good hiding place, they're happy and I only get the occasional stems uprooted. If they don't--well, it's a matter of replanting over and over and over and over.