:Do these walls extend below the surface? If not, you might get some turtles digging out under the RR ties. Maybe get some pieces of slate to line the inside walls to prevent digging next to the RR tie walls.
They are a couple of inches below the ground. In a year, I havent had any problems with them digging under the railroad ties. The only problem I had was them climbinb up the corners, but that was solved by putting stepping stones in all of the corners. The ground by the ties is very hard and full of gravel, so they don't dig in it. Just today I expaned the pen, making it approximately 400 square feet. There is so much room for them to explore that they dont even hang around the sides of the pen.