Please add an option to block walls and buildings. Very often i move them without notice (especially walls). It could be easily done without any additional icon. We could just use "Layout editor" icon, and make it two-state button: 1st, depressed (by holding for 2 seconds) when the buildings are locked, and 2nd, when you can move them.
Here is an example, how it can look like:
http://i.imgur.com/rLACBH3.gif

