>>513326588
in that comment I was talking about transnistria.

Now that you mention the Dnieper being the best defensive line, it might be true, that they should put the main line behind there. Beyond that is just farmland and a few little villages, but for the security of their coast line they should still aim to get that little piece. For example the port of Mykolaiv (where a sunken Ukrainian warship lies) would be blocked by a single gun in case of hostility.

I found a convenient irrigation channel on google maps. It is 90m wide, they would only have to extend it a little bit to the ocean.