Bill's in river, a place one won't sink (4,3)
I believe the answer is:
dead sea
'one won't sink' is the definition.
I can't judge whether this definition defines the answer.
'bill's in river a' is the wordplay.
'bill's' becomes 'ad's' (advertisement stuck on wall).
'in' indicates putting letters inside.
'river' becomes 'dee' (River Dee).
'ads' inserted within 'dee' is 'deadse'.
'deadse'+'a'='DEAD SEA'
'place' acts as a link.
Can you help me to learn more?
(Other definitions for dead sea that I've seen before include "Middle East saltwater lake, almost 1,300 feet below sea level" , "Inland salt lake on Israel-Jordan border" , "Salty lake on the Israel/Jordan border" , "large salt lake" , "World's lowest lake" .)