[micwag]

That's only true for bigger changes, at least in europe borders are changing quite frequently on a microscopic level. For example the border between Switzerland and Germany changed by a couple of meters this year. The same happened with the German-Austrian and German-Czech(ian?) border in the last couple of years.

Germany has border "disagreements" with half of its neighbours. Some are bigger like lake constance (Switzerland&Austria) and the ems delta (Netherlands). Some are smaller like the Vennbahn (Belgium).

Some of Germanys border is also shared as a Condominium with its neighbours (Switzerland, Austria, Luxemburg).

And finally Denmark and Germany have a land border but not a sea border