hey, i have u. tricolor, u. longifolia, u. monanthos?, and i believe u. praelonga. i could be wrong on the last 2....lol. they all are growing well and dont really get trampled. you can plant them at the bottom of the tank. or, if you have a water source comming from the background, you can create pockets of peat around the water source and plant them there. make sure there is water slightly flowing into the pocket. there are also epiphytic species that you get to grow on a mossy peice of wood or background. very cool plants with incredibly orchid like flowers.
livida or sandersonii would be excellent ground covers and very easy to grow! whatever you decide on, avoid subulata!!!!!! its a weed and will take over and kill other small plants!! trust me, you dont want it!