Trim outside boundary with the EXTRIM command
Many thanks to Dave Murchison for finding the EXTRIM command, and sharing it with me. This command is basically an extension to the TRIM command. With this command you can select a boundary to trim back all objects to. This is great for clipping back construction lines etc back to the limits of whatever it is you're drawing. Bear EXTRIM in mind in future as it clearly has great potential for saving a lot of time.