The second one is charging hourly. We tend to prefer hourly fees on projects that are particularly open ended or very small scope. Our hourly rates are currently between $60 and $120 per hour depending on who is doing the work.
The word sonder exists, though. It means to probe, and in a more specific use, to test the depth of something. The word sound (as in the water feature) is a cognate, both related to the Old English sund meaning to swim, or the sea. I can't really think of an English equivalent that's specific beyond mere awareness.
Origin of Son, Meaning of Son. Origin: In Danmark this is the form for 'son of Matthias'. This kind of name-giving was also in use in Schleswig (Northern part of Germany, which was until 1866 integral part of Danmark). Somehow in the 17th or 18th century surname became mandatory, so in that time the male ancestor was called Matthias.