The canals also help a lot.

In my over four years in Amsterdam I've never seen anyone pee into the canals outside of queen's day (a day-long city-wide parade/giant party, for those who don't live here).

German cities are full of public urinals such as the ones you describe. The problem is that they are quickly soiled making them unappealing, even for the most drunk revellers. The only way the behaviour can be curbed is with big fines - it works in the UK for the most part.

Or maybe they could come up with an efficient way to clean the public urinals instead.

That is true but then your average drunk would still choose the path of least resistance which is usually the nearest bush, wall or tree. We are genetically wired to look for the easiest solution which would of course be peeing wherever we are when nature calls. The only thing that stops us from exhibiting this behaviour when sober is inhibition. When alcohol numbs our inhibitions and sense of risk we revert to our most primal selves and in some cases that means we piss in places we should not piss in.