Hello Andy,
If you have been looking for a way to lock elements of the layout, such as boxes and text, I have been looking to do the same thing, but I have not found any feature that allows that. I don't think it exists, but if you find a way, please share it! It would be such a good feature.
The best trick that I have found so far is for textboxes, lines, and shapes such as rectangles. I snap them to guidelines. I makes them harder to move accidentally.
Good luck!