This video demonstrates using the Create Terrain Model Boundary tool to add a Boundary element to a Terrain in order to preserve edge triangle edits. Also, the Remove Terrain Model Boundary tool is shown.
Click the video below to play it. To view in fullscreen mode, first click the YouTube link at the bottom of the video to launch the video on the YouTube site. Then, click the fullscreen button (rightmost button at bottom of video).
Recorded in 1280 X 720 resolution.