Terrain barriers

I have just solved the problem of the player falling into the lake and/or off the terrain by placing cubes at the sides of the terrain and turning off the mesh renderer. I placed a plane on top of the water of the lake and again turned off the mesh renderer, and the controller can now happily traverse the lake should he/she so wish. I feel like I've solved a lot of issues today. My website and Unity application are now more or less complete, I just have to iron out a few more issues. Nearly there! (I hope.)