Protection is only possible, if you ask Navico for "toolkit partnership". It's cost about 1.000 USD.
For free is only the possibility to set an expiration date with the IMC. The user cannot use the chart after expiration of the date. This is helpful, but not 100% secure.
Your depth values: I hope you have a shape with all depth lines together. I also must know the line value distance (i hope ever 0,1 m between two lines)
For help i need the value from the shoreline and the value from the greatest deep. The rest is editing in the attribute table. You also can send us the shape file, other users we also help withe there original files and we respect your data protection rights (contact LUKE, the admin, not load the files into the forum).