Bounders impounding river ferries (2-3)
I believe the answer is:
ro-ros
'bounders' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'impounding river ferries' is the wordplay.
'impounding' indicates putting letters inside.
'river' becomes 'r' (abbreviation for river).
'ferries' becomes 'roos' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'r' inserted into 'roos' is 'RO-ROS'.
Can you help me to learn more?
(Another definition for ro-ros that I've seen is " Car ferries".)